Do We Need Pythagoras Here?

Geometry Level 1

If lines l l and m m are parallel, then what is the value of angle x x (in degrees)?


The answer is 35.

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57 solutions

Krishna Garg
Jul 24, 2014

Since the straight lines n n and m m are perpedicular to each other, then the angle coloured in orange is a right angle.

On the straight line m m , angles y y^\circ and 12 5 125^\circ must add up to 18 0 180^\circ . So y + 12 5 = 18 0 y^\circ + 125^\circ = 180^\circ or y = ( 180 125 ) = 5 5 y^\circ = (180 - 125)^\circ = 55^\circ .

The sum of angles in the triangle adds up to 180 degrees:

9 0 + x + 5 5 = 18 0 , x = ( 180 55 90 ) = 3 5 90^\circ + x^\circ + 55^\circ = 180^\circ \quad,\quad x^\circ = (180 - 55 - 90)^\circ = 35^\circ

Hence, x x equals 35 35 .

Jonathan Moey
Jul 24, 2014

125 = x + 90 , x = 35 125= x+90 \quad,\quad x=35

In response to jonathan moey; Thank u another method is 125-90is 35

abudahir 617 - 5 years, 6 months ago

This is the exterior angle property I suppose?

Avinash Kamath - 5 years, 6 months ago

From my figure, since y y and 12 5 125^\circ are supplementary angles, we have

y + 125 = 180 y+125=180 \implies y = 180 125 = y=180-125= 5 5 55^\circ

Since the sum of the interior angles of a triangle is 180 180 , we have

x + y + 90 = 180 x+y+90=180 \implies x + 55 + 90 = 180 x+55+90=180 \implies x + 145 = 180 x+145=180 \implies x = 180 145 = x=180-145= 35 \boxed{35}

Lee Ling Yan
Jul 25, 2014

There is an alternate angle. The 125 is alternate to angle x + the 90degrees there as the lines L and P are perpendicular .

125+55=180 hence 90-55=35

Karishma Mahanta
Jul 28, 2014

sum of opposite interior angles=exterior angle n+90=125 n=125-90=35

Nicolas Bryenton
Jul 23, 2014

Let m be the other angle in the triangle. This angle is supplementary with 125, therefore

125 + m = 180 125+m=180

m = 180 125 = 55 m=180-125=55

Also, line pv is perpendicular to vm, therefore, the angle in the triangle at v is 90. According to the angle sum theorem,

m + n + 90 = 180 m+n+90=180

n + 90 + 55 = 180 n+90+55=180

n = 180 145 = 35 n=180-145=35

there are two solutions the first is 125-90=35 and the second is 180-(55+90)=35

Noor Mohamed - 6 years, 10 months ago
Kids Force
Aug 1, 2014

How I found the solution: First look at line m, and you see that you have 125 degrees and the other side is its supplement (Line M is Supplementary), which is 55 degrees. Then, you see the right angle, and you see that line v is perpendicular to line m which then tells you that this angle is 90 degrees. Therefore, 90 + 55 + X= 180 degrees x=35 degrees and that's how I got it.

Julieta Ramos
Jul 24, 2014

n=180-( (180-125)+90) = 180-(55+90)=35

Pruthvi Raj J S
Jul 24, 2014

We know that half angle of the circle is 180 degree On line 'm' outer angle is 125 degree. so, 180 - 125 = 55 degree (Which is inner angle now) Since 'P' is perpendicular to 'm' the angle is 90 degree. Now Remaining angle to find is 'x'
Total angle of triangle is = 180 degree ; x = ? ; Inner angle = 55 degree ; Perpendicular angle = 90 degree ;

i.e., 180 = x + 90 + 55, 180 = x + 145, x = 180 - 145, x = 35

Why r u even trying so much Simple Its Exterior Angle Property 9 0 o + x = 12 5 o 90^o + x = 125^o x = 12 5 o 9 0 o x = 125^o - 90^o x = 3 5 o x = 35^o

Mihir Srivastava - 6 years, 10 months ago

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When you are writing solutions to easier problems it is important to be explain your steps very clearly. It is obvious to those who know how to solve this type of problem, so a solution like yours would make sense, but someone who does not understand the problem would learn nothing from it.

Nicolas Bryenton - 6 years, 10 months ago

Its easy method

Bazmi Farooquee - 6 years, 10 months ago

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you writing is nice

Gaurav singh - 6 years, 10 months ago

18 0 12 5 = 5 5 180^\circ-125^\circ=55^\circ by the rules of straight lines a + b = 18 0 a^\circ+b^\circ=180^\circ

9 0 5 5 = 3 5 90^\circ-55^\circ=\boxed{\large{35^\circ}} by the right triangle rules a + b + 9 0 = 18 0 a + b = 9 0 a^\circ+b^\circ+90^\circ=180^\circ \implies a^\circ+b^\circ=90^\circ

Phạm Hoàng
Jul 3, 2018

First 180 125 = 55 180-125=55 .Next we see that line m m & line l l are parallel so the third straight line are 9 0 90^\circ to line m m .So x + 90 + 55 = 180 x = 180 90 55 = 180 ( 90 + 55 ) = 180 145 = 35 x+90+55=180 \implies x=180-90-55=180-(90+55)=180-145=\color{#3D99F6}\boxed{\large{35}}

Larisa Altshuler
Dec 26, 2017

The problem is overdetermined. It is does not matter whether lines m and l are parallel or not parallel. The exterior angle of a triangle of 125 degrees is equal to the sum of x and 90 degrees.

Two supplementary angles add up to 18 0 180^\circ . The supplement of 12 5 125^\circ is 180 125 = 5 5 180-125=55^\circ . So the unknown angle is 90 55 = 90-55= 3 5 \boxed{35^\circ}

We know that a straight line is consist of 180°.In the above picture we can see that one part of the line is 125°.So another part must be 180°-125°=55° Then x =180°-(55°+90°) =35°

Refath Bari
Jun 29, 2016

In order to find m x m\angle x , we must find the measure of the other two angles in our triangle.

This can be done by finding the measure of the angle adjacent to the m 125 m\angle 125 angle:

180 125 = 55 180 - 125 = 55

Our second angle, which is adjacent to a right angle, must also be a right angle of 90 O { 90 }^{ O } .

Therefore, we can conclude that the measure of m x m\angle x can be found by:

m x = ( 180 ( 55 O + 90 O ) m\angle x = (180 - ({ 55 }^{ O }+{ 90 }^{ O })

Where m x = ( 180 ( 55 O + 90 O ) m\angle x = (180 - ({ 55 }^{ O }+{ 90 }^{ O })

And m x = ( 180 ( 145 O ) m\angle x = (180 - ({ 145 }^{ O })

Therefore, m x = 35 O m\angle x = { 35 }^{ O }

Q E D Q\bullet E\bullet D

Daniel Feng
May 30, 2016

You see a 90 degree angel below the triangle, so that means that one of the angles of the triangle has to be a 90 degree angle, since l and m are parallel. The 125 degree angle only makes up a part of the 180 degree angle, so the other angle is 55 degrees. 90+55=145, and 180-145 is 35.

Youssef Hassan F
Dec 13, 2015

Vino Vishwa
Dec 4, 2015

The given triangle is right angled triangle So x+90°=125° x=125°-90° x=35° This is the correct angle for x

Luvneesh Kumar
Nov 16, 2015

No Pythogoras is not needed :)

Achille 'Gilles'
Nov 1, 2015

Bala Murugan
Oct 28, 2015

We don't need Pythagoras here. Just the angles.A straight line forms 180 degree.If one angle is 125 degree,then remaining angle will be 180-125=55 degree. X is one of the angles of a triangle. 55 we found is also another angle of the same triangle.Opposite to the x is a perpendicular angle of the triangle.It forms angle of 90 degree.A triangle also forms the total of 180. Therefore, x+55+90=180 degree. x+145=180. x=180-145=35 degree.

Shrivatsa Joshi
Oct 19, 2015

Alternate interior angles are equal. So 120-90=35

Jonas Capili
Oct 10, 2015

Linear pair are supplementary, therefore 180-125=55 55+90=145 And since the sum of the angles of any triangle is 180 (180-145=35)

Siva Meesala
Oct 5, 2015

X is 180-55-90 is 35.

Sherilynne Ruiz
Sep 26, 2015

180-125=55 90+55=145 180-145=35

Nirupam Choudhury
Sep 22, 2015

By exterior angle property 125-90=35

Fitri Pitsus
Sep 7, 2015

x degrees= 180-90-(180-125)= 35 degrees

Line M forms a 180 degrees since its a supplementary angle. We see that the right side is 125 degrees. We need to find the other side because we cannot solve for x without it. The left side is = 180 - 125 = 55 The second angle is 90 degree since it is perpendicular. We can now find the angle of x by adding the 2 angles - 180 degree (Any triangle has a sum of 180 degree) x = 180 - (55+90) = 35 degrees

Tushar Kaushik
Aug 10, 2015

External angle property SUM OF TWO INTERNAL ANGLES IS EQ TOVEXTERNAL ANGLE

Alternative interior angles in the parallel linens are equal So, 90 + X = 125 X = 125 - 90 X = 35

Gourab Roy
Jun 11, 2015

Is the problem from the book ( for class 9) of R.D. Sharma, isn't it ?

Rigel Kent Tormon
May 12, 2015

Since line p is perpendicular to point q, we can deduce that it creates a 90 degree angle. Since the angle with the measure of 125 and the angle inside the triangle create a linear pair, we can apply the linear pair postulate, which states that if twig angles form a linear pair, then they're supplementary. Supplementary angles have a sum of 180. To get the interior angle adjacent to the aforementioned angle, simply subtract 125 from 180, 180 — 125 = 55. We can add this to the other angle whichhas a measure of 90 degrees. Since all triangles have interior angles that sum up to 180, we can add the two angles and subtract it from 180 to get the measure of the last angle. 90+55=145. Subtract this from 180, 180—145=35. To check if this is correct, just add the measures of the interiors of the triangle and, if they equate to 180, your asnwer is correct. In this case, 90+55+35=180.

Sumanth Girish
May 5, 2015

Let A=n, B=90 deg.(because it is right angled triangle) and C=180-125(because angle formed on a st.line=180 deg.). Now we got B=90 degree and C=55 deg.. Therefore, A+B+C=180 deg. ; A+90+55=180; A+145=180; So, A=180-145=35 deg.

Tania Brown
May 3, 2015

Find the two angles of line M.
180-125= 55 Now find the missing angle in triangle. Triangle angles must equal 180. As a a right angle one of them is 90.
90-55= 35

Shane Powell
Apr 15, 2015

180-125=55. 90+55=145. 180-145=35

Ganesh Naik
Jan 26, 2015

"exterior angle is equal to sum of the interior opposite angles" is the theorem behind this..\

x=90-(180-125)

Vishal S
Dec 14, 2014

We know that in a triangle exterior angle is equal to the sum of opposite angles. therefore n+90=125 => n=125-90 => n=35 therefore n=35degrees

In the given fig, PQR (suppose R a point from P) forms a triangle. In triangle, PQR , exterior angle PQM = interior angle RPQ + interior angle PQR. ( exterior angle = sum of interior angles) so, 125 degree = x + 90 degree (PQ is perpendicular to m ) 125-90=x 35 degree = x

Ericroel Archival
Sep 21, 2014

It seems that the total degrees of a triangle is equals to 180,and the adjacent angle of this is 125.Then this will be 180-125=55 and it seems that this is a right triangle so, 55 will be added to 90 for you to be able to get the remaining angle which is N=? so,55+90=145.Then my solution of this will be N=180-55-90 N=35.

Hon Ming Rou
Aug 28, 2014

180 - 125 = 55

90 - 55 = 35

125 is the same as n+90 because of the Z way of solving this because they are perpendicular lines. So then 125-90 is 35 (which is the real answer)

Evan Lee
Aug 15, 2014

Since line l and line m are parrallel we have alternate interior angles. 125-90*=35 ……….. *90 degrees is from the perpendicular line f

180-125=55, then 55+90= 145...therefore 180-145=35... so 35 is the correct answer.

Shaaf Farooq
Aug 6, 2014

Easy. 180-125 to find the remaining angle which gives us 55. 55 is adjacent to the line L and P is perpendicular so its 90 and 90 + 55 gives us 145. Now that the whole angle equals 180. The angle remaining aka angle X would be 180-145 which gives us 35 which is our answer. Shaaf Farooq from Canada

Himanshu Mishra
Aug 3, 2014

Using the property that in a triangle the sum of 2 interior angles is equal to the exterior angle formed on the opposite side, solution can be found out as 90+x=125 => x=35

Dharmendra Kumar
Aug 2, 2014

n=90-(180-125)= 35

Abhishek Verma
Jul 30, 2014

By the property of exterior angle which is equal to the sum of two opposite interior angle we can say that 90+x=125,Therefore x=35

Jeremiah Valle
Jul 30, 2014

125 degrees plus the angle adjacent must equal 180 degrees
180 - 125 = 55 degrees The sum of all three angles within a triangle must be 180 degrees as well. Since we know line (p) is perpendicular to lines (l) and(m) that gives us our second angle where line (p) and (m) intersect, which is 90 degrees. n= 180 - (90 + 55) answer: angle (n) is 35 degrees.

Asutosh Mukharjee
Jul 29, 2014

l and m are parallel making angle 180-125=55 and at point q making 90 so 180-(55+90)=35

Naveen Sekar
Jul 27, 2014

too easy question.. (180-125) = 55.......triangle = 180 deg......90+55+n = 180........n = 180-145......therefore n = 35

Kim Diate
Jul 26, 2014

remember that the sum of the interior angles of a triangle is 180, Case solved.

Ng Donn
Jul 25, 2014

125 = 90 + x. Therefore x = 35.

Sachrit Johri
Jul 25, 2014

There is a rule, if you have a triangle with angles A,B,C, and if there is an angle D such that C=180-D then D = A+B

You can do it the long way to prove this but it is easier to just memorize it :P

Sachrit Johri - 6 years, 10 months ago

We know pq is a perpendicular. Since 125 is an external angle, x=125-90=35.

y = 18 0 12 5 = 5 5 y^\circ = 180^\circ - 125^\circ = 55^\circ

x = 9 0 5 5 = 3 5 x^\circ = 90^\circ - 55^\circ = \color{#D61F06}\boxed{35^\circ}

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