If a and b are the roots of the equation x² – 9x + 20 = 0, find the value of a² + b² + ab?

A. -21
B. 1
C. 61
D. 21

Explanation:

a² + b² + ab = a² + b² + 2ab – ab
i.e., (a + b)² – ab
from x² – 9x + 20 = 0, we have
a + b = 9 and ab = 20. Hence the value of required expression (9)² – 20 = 61.

Correct Answer: 1 ✔

Last Updated: February 08, 2020