If a-b=3 and a2+b2=29, what is the value of ab?
A
10
B
12
C
15
D
18
Correct Answer: 10
a2 + b2 = 29 ( a - b)2 + 2ab = 29 3a2 + 2ab = 29 9 + 2ab = 29 2ab = 29 - 9 2ab = 20 ab = 10