Problem: If r and s are the roots of the equation ax2+bx+c=0, the value of r21​+s21​ is:
Answer Choices:
A. b2−4ac
B. 2ab2−4ac​
C. c2b2−4ac​
D. c2b2−2ac​
E. none of these answers
Solution:
Since r21​+s21​=r2s2r2+s2​=(rs)2(r+s)2−2rs​, and since
r+s=−ab​ and rs=ac​, we have r21​+s21​=c2b2−2ac​