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Algebra Level 5

If the roots of the equation x 2 10 a x 11 b = 0 x^2-10ax-11b=0 are c c and d d and those of x 2 10 c x 11 d = 0 x^2-10cx-11d=0 are a a and b b , then find the value of a + b + c + d a+b+c+d where a , b , c , d a,b,c,d are all distinct numbers.


The answer is 1210.

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1 solution

Rishabh Jain
Jun 26, 2016

Relevant wiki: Vieta's Formula Problem Solving - Intermediate

Using Vieta's on first and second equation: c + d = 10 a , a + b = 10 c c+d=10a~,~a+b=10c

Adding we get:- a + b + c + d = 10 ( a + c ) . . ( 1 ) a+b+c+d=10(a+c)..(1) Subtracting we get:- b d = 11 ( c a ) . . ( 2 ) b-d=11(c-a)..(2)

Since c c is a root of first equation: c 2 10 a c 11 b = 0 \implies c^2-10ac-11b=0 and since a a is a root of second equation: a 2 10 a c 11 d = 0 \implies a^2-10ac-11d=0

Subtracting these two we get:- c 2 a 2 = 11 ( b d ) = 121 ( c a ) c^2-a^2=11(b-d)=121(c-a)~ (Using 2 2 ) c + a = 121 \implies c+a=121 Substituting in 1 1 we get:-

a + b + c + d = 10 ( 121 ) = 1210 a+b+c+d=10(121)=\boxed{1210}

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