Thursday, December 20, 2012

Q12/130) What is the sum of the squares of the roots of the equation x^2 - 7[x] + 5 = 0?



7[x]>  =  7x
hence any solution must satisfy the quadratic equation
x^2 - 7x + 5 <= 0
So x is between 0.8 and 6.2.(approximate)
It follows that the possible values of [x] are 0 to 6. So we need to check for of [x] from 0 to 6 and find x to be in proper range

There are altogether 4 distinct solutions.

They are sqrt(2), sqrt(23), sqrt(30), sqrt(37)

The sum of their squares is 2 + 23 + 30 + 37 = 32+60 = 92

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