Problem: For one root of ax2+bx+c=0 to be double the other, the coefficients a,b,c must be related as follows:
Answer Choices:
A. 4b2=9c
B. 2b2=9ac
C. 2 b2=9a
D. b2−8ac=0
E. 9b2=2ac
Solution:
roots p,q where p=2q
p+q=3q=a−b;9q2=a2b2
pq=2q2=ac;2q2=ac
29=acb2 or 2b2=9ac