A point and an equation

Algebra Level 3

there is a point on the cartesian plane, which, when joined to the origin, makes an angle of 4 5 45^\circ with the x axis.

the coordinates of this point is ( a , b ) (a,b) , and a a and b b are the zeroes of the equation c x 2 + d x + e = 0 cx^2+dx+e=0 and e x 2 + d x + c = 0 ex^2+dx+c=0 .

it is provided that d < 0 d<0 and c > 0 c>0 .

find c+d+e+1.

0 1 4 3

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1 solution

Shivam Rajoriya
Sep 30, 2014

here it is given that the line joining the point and the origin is 4 5 45^\circ therefore tan 4 5 = b a \tan45^\circ=\dfrac{b}{a} .

hence, a = b a=b .

as both the equations have same zeroes.

that is why, c a 2 + d a + e = e a 2 + d a + c ca^2+da+e=ea^2+da+c

from this equation we get c = e c=e ,

as the equation has equal zeroes, d 2 4 c e = 0 d^2-4c\cdot e=0

hence, d 2 4 c 2 = 0 d^2-4c^2=0 -----------(as c = e c=e )

from the above equation we get d = ± 2 d=\pm2 --------(as d < 0 d<0 and c > 0 c>0 )

d = 2 c d=-2c , therefore, c + d + e = 2 c 2 c = 0 c+d+e=2c-2c=0 --------(as c = e c=e and d = 2 c d=-2c )

hence, c + d + e + 1 = 1 c+d+e+1=\fbox{1}

Edited you question to use L a T e X LaTeX and changed " (here by mistake if your answer is 0 then mark it 1, if 1 then 0, if 2 then 3 and if 3 then 2)" to "find c+d+e+1".

You can click on the edit button to view what I have changed.

Kenny Lau - 6 years, 8 months ago

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no it is correct

shivam rajoriya - 6 years, 7 months ago

Problems regarding your solution: what if ( a , b ) = ( 1 , 1 ) (a,b)=(1,-1) ? It would still make an angle of 4 5 45^\circ with the x-axis, but a b a\ne b . You need to explain why this cannot be the case.

Kenny Lau - 6 years, 8 months ago

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yes you are right. It is mentioned that e and c are both greater than 0 whose ratio is the product of two numbers a and b it can only be positive if both the numbers are either positive or negative..

shivam rajoriya - 6 years, 7 months ago

I also edited your title. You can suggest a better title, but please do not name the problem using your name.

Kenny Lau - 6 years, 8 months ago

shivam rajoriya this question is made by me

shivam rajoriya - 6 years, 8 months ago

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it is a nice joke

Gajender Singh - 6 years, 8 months ago

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