The Right Triangles

Geometry Level 1

In the image above, Z W X Y , \overline { ZW } \bot \overline { XY }, X W = 16 \overline { XW } =16 and W Y = 9 \overline { WY } =9 . Find Z Y + X Y \overline { ZY } +\overline {XY }


The answer is 40.

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21 solutions

William Li
Nov 13, 2014

Use similar triangles. ZY / 25 = 9 / ZY , ZY^2 = 225 , ZY = 15.

 We know XY as 25, so just add ZY with XY, which is 40.

Duh, it helps to read the question. I solved for XZ + ZY instead of ZY + XY.

Michael Frey - 4 years, 10 months ago

let ZY be x..... and apply pythagorus theoram to rt. triangle ZWY, therefore, ZW^2=(x^2-81)

Now apply pyth. theoram to rt. triangle ZWX,

it gives, XZ^2=x^2+175

Now finally apply pyth. theoram to rt. triangle XZY, it gives XY^2=XZ^2+YZ^2 i.e. 25^2=x^2+175+x^2

YZ=x=15 so, XY+ZY=25+15=40 ANSWER

Hoo Zhi Yee
Nov 13, 2014

By angle chasing, triangle X W Z XWZ and triangle Y W Z YWZ are both similar to triangle X W Z XWZ . Thus W Z 2 WZ^{2} = ( 16 ) ( 9 ) (16)(9) = 144 144 and W Z = 12 WZ=12 . Therefore by Pythagoras Theorem we have Z Y = 15 ZY=15 and thus Z Y + X Y = 15 + 16 + 9 = 40 ZY+XY=15+16+9=40

Alvin Vasquez
Nov 13, 2014

The value of ZY is equal to the square root of the product of WY and XY. . . Substituting the values we acquire ZY as 15 so 15 + 25 = 40!

Adam Gawronski
Dec 20, 2017

If xy & zy are viewed as vectors then the answer is zx ie. 20

Roland Copino
Nov 15, 2014

Notice that it is a right triangle, and the hyp of it is side xy (which is 16+9=25)

Therefore.. a²+b²=c² ... So, c= 25 .. C²= 625.. There are only two numbers which satisfies the eq.. 20 and 15.. Since were looking for the shorter side.. Therefore , xy= 25 , equal 25+15 = 40

not only 20 and 15 but 15 × 2 15 \times \sqrt{2} and 5 × 7 5 \times \sqrt{7}

Sharan Raj - 6 years, 6 months ago
Robert Haywood
Nov 14, 2014

Here's how I solved it. When I saw this problem, the first thing I noticed was that 16 and 9, multiples of 4 and 3, added up to 25, a multiple of 5. 3-4-5... The simplest Pythagorean triple! I ended up disregarding all actual math and chasing after a solution of triples...

To find ZY, we need to utilize the Pythagorean Theorem. Before we can do THAT, we need to find a value for ZW that works for both triangles. The first thing I noticed was that ones of the legs of Z X W \triangle ZXW was 16, which is a multiple of 4. 4 4 = 16 4*4=16 , so I knew it was possible that the lengths of the sides might have been part of a Pythagorean triple created by multiplying 3-4-5 by 4. If this was true, that would mean that ZW would be 12. This once again opens up the possibility of a Pythagorean triple, but created by multiplying 3-4-5 by 3 instead of 4 (This is for Z X Y \triangle ZXY ). If this is true, that means the hypotenuse is 15 ( 5 3 5*3 ...).

I can check my answer now by doing the same thing for ZX... ( 5 4 = 20 5*4=20 ), causing the two legs of Z Y X \triangle ZYX to be equal to 15 and 20. Wait a minute... This seems to me to be yet ANOTHER Pythagorean triple, created by multiplying 3-4-5 by 5! This means that XY would be 25 since it is the hypotenuse... and sure enough, it is!

So now I've got ZY (15) and XY (25), and all I have to do is add them to get 40!

A multiple of a Pythogorean triple is another Pythogorean triple. So it is no coiincidence multiplier everything with 5 gets the answer. It's how i solved it too.

Peter van der Linden - 4 years, 9 months ago
Palash Som
Nov 13, 2014

this can be done by using the similarities in the triangle .

we know that when any perpendicular is drawn from the the right angle of a triangle to its hypotenuse then all the triangles become similar .

so we can say that 16/zw = zw / 9 solving we get 144 = zw ^2 and so by solving it further we get the answer (40)

Paul Patawaran
May 13, 2018

Letting XY=a and XZ=b

Now by use pythagorean theorem for [XYZ], we can see that a^2+b^2=625 ........ (i)

Use pythagorean from [XWZ] and [YWZ], gives

ZW^2 = b^2 -256 ZW^2 = a^2 -81

Equating thees two equations to obtain, b^2-256 = a^2 -81 a^2 -b^2 = -175, compare this into (i) gives,

2a^2 = 450 a^2 = 225, since a>0

So a=15, this implies ZY is 15 units

So, ZY+XY=15+25=40

Altitude(height) theorem

In a right triangle Δ Z X Y \Delta ZXY the altitude Z W \overline {ZW} fulfills : Z W 2 = 16 9 = 144 Z W = 12 Z Y 2 = 144 + 81 = 225 Z Y = 15 \overline {ZW}^2 = 16 \cdot 9 = 144 \Rightarrow \overline {ZW} = 12 \Rightarrow \overline {ZY}^2 = 144 + 81 = 225 \Rightarrow \overline {ZY} = 15 ...

Joe Potillor
Oct 5, 2016

ZW is the geometric mean of XW and WY, and if you do that, you'll get 12 for ZW. From that, you use pythagorean's theorem, to get ZY of 15, and adding it to the known side of XY which is 25, you will get 40

Ramesh Perumal
Dec 3, 2014

XY=25 YZ=y XZ=p WZ=x p^2=x^2+〖16〗^2 y^2=x^2+9^2 p^2+y^2=2x^2+〖16〗^2+9^2 〖25〗^2=2x^2+〖16〗^2+9^2 x^2=9×16 x=12 p=20 y=15 XY+YX=25+15=40

Siddharth Singh
Nov 28, 2014

ZW^2+16^2=ZX^2 ...1 ZW^2+9^2=ZY^2 ...2 adding 1 and 2 2ZW^2+256+81=ZX^2+ZY^2 2ZW^2+337=(16+9)^ (ZX^2+ZY^2=25^2) 2ZW^2=625-337 2ZW^2=288 ZW=144^1/2 ZW=12 ZW^2+WY^2=ZY^2 12^2+9^2=ZY^2 ZY+XY=15+25=40

Luka Srot
Nov 23, 2014

|ZW|^2 + |XW|^2 = |ZX|^2

|ZW|^2 + |WY|^2 = |ZY|^2

|ZX|^2 + |ZY|^2 = |XY|^2

Add first to equations together and substitute |ZX|^2 + |ZY|^2 you get on the right side for |XY|^2. Solve for |ZW|, then plug the value in the second equation. You obtain |ZY|=15, add 25 and that's it

Curtis Clement
Nov 21, 2014

Triangles XZW and WYZ are similar with angle(ZXW)=angle(WZY). So if we let ZW=H: 9/H=H/16, so H^2=9*16=144, therefore H=12. Now we use pythagoras, with the 3,4,5 triangle to find that XZ=20 and ZY=15. Hence, ZY +XY=15+25=40.

Mira Stefan
Nov 20, 2014

in triangl WYZ : cos Y =9/ZY
intriangle XZY : cos Y =ZY/25
9/ZY =ZY/25
ZY power 2= 225
ZY =15
ZY + XY = 15 +25 =40




Swagath N Shaji
Nov 15, 2014

Let ZW=X , ZY²=9²+X²=81+X² , XZ²=16²+X²=256+X² , ZY²+XZ²=81+256+X²+X²=337+2X² , According to Pythagorus theorom , ZY²+XZ²=XY²=(16+9)²=25²=625 , 337+2X²=625 , 2X²=625-337=288 , X²=288/2=144 , X=√144=12 , ZW=12 , ZW²+WY²=ZY² , ZY²=12²+9²=144+81=225 , ZY=√225=15 , ZY+XY=15+25=40

Youssef Mohsen
Nov 14, 2014

(ZW)^=9*16=144 (ZW)=12 (ZY)^2=9^2+12^2 (ZY)^2=225 (ZY)=15 (ZY+XY)=15+(9+16) =40

Ankit Mohanta
Nov 14, 2014

perpendicular to hypotenuse is ZW so we can write ZW^2=16*9 ZW=12 and Zy^2=12^2+9^ ZY=15 therefore ZY+XY=15+25=40

Vinit Béléy
Nov 14, 2014

XY = XW + WY = 16 + 9 = 25 Since ∆XZY is a right triangle, we can expect it to follow one of the right triangle triads: 3,4,5 Since XY = 25 = 5 x (5) ; ZY = 5 x (3) ; XZ = 5 x (4) (from the right triangle triad 3,4,5)

Therefore ZY = 15;

ZY + XY = 25 + 15 = 40

Nitika Agarwal
Nov 14, 2014

Appying Pythagoras Thm.
WZ^2 = XZ^2 - 16^2 WZ^2 = ZY^2 - 9^2 From Above Two Eq. We Get XZ^2 -ZY^2 = 175

Applying Pythagoras Thm Again we Get XZ^2 + ZY^2 = 625

Solving Eq. 3 nd 4 We Get XZ=20 YZ=15

So XY + YZ = 40

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