If a+b=13 and a-b=3 , then find the value of a2+b2
A
69
B
79
C
89
D
91
Correct Answer: 89
(a2 + b2) = 1/2 {(a + b)2 + (a - b)2} = 1/2 {(13)2 + (3)2} = 1/2 (169 + 9) = 1/2 * 178 = 89