Find the value of a/b + b/a, if a and b are the roots of the quadratic equation x2 + 10x +5 = 0?  Choices.
A) 6
B) 42
C) 24
D) 18
E) 95

Rationale: a / b + b / a = ( a 2 + b 2 ) / ab = ( a 2 + b 2 + a + b ) / ab = [ ( a + b ) 2 - 2 ab ] / ab a + b = - 10 / 1 = - 10 ab = 5 / 1 = 5 hence a / b + b / a = [ ( - 10 ) 2 - 2 ( 5 ) ] / 5 = 90 / 5 = 18 . d )
Answer: D