Unique Quadrata

Algebra Level 4

a , b , c , d a, b, c, d are distinct numbers such that:

  • a a and b b are the roots of the equation x 2 2 c x 5 d = 0 x^2-2cx-5d=0
  • c c and d d are the roots of the equation x 2 2 a x 5 b = 0 x^2-2ax-5b=0

Find the value of a + b + c + d a+b+c+ d .


The answer is 30.

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1 solution

Aakash Khandelwal
Jul 25, 2016

a + b = 2 c , c + d = 2 a , a b = 5 d , c d = 5 b a+b=2c , c+d=2a , ab=-5d , cd=-5b

Therefore a c = 25 , a + c = b + d ac=25 , a+c=b+d

Thus req. value is 2 ( a + c ) 2(a+c)

Satisfying a and c in respective quadratic equations , and adding resultant quads, we get a quad in (a+c).

Equations give value of a+c= 15 a n d 20 15 and -20 .

Answer follows after that.

nice question , enjoyed solving it ,,,

Rudraksh Sisodia - 4 years, 10 months ago

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