Let A, B, where A, B (- 2, 2 ), be the roots of the quadratic equation x2-2x-5=0. Then 20 2 ( A+B2 ) is equal to :
- 10+ 10
- 10-2 10
- 10-3 10
- 10- 10
Answer
(3) 10-3 10
Solution
A+ B=2, A B=-5
(A+B)= 21-(-5)= 13
Roots are 1 6: A=1+ 6>0, B=1- 6<0
A (0, 2 ), B (- 2, 0 ) A+B (- 2, 2 )
(A+B)= 13>0 (A+B)= 3 10
20 2 ( A+B2 )=10 (1- (A+B) )
=10- 30 10=10-3 10
Answer: (3)