Q538
If a + b = 5 and ab = 3, then (a3 + b3) is equal to:
A.
70
B.
75
C.
80
AnswerD.
65
Answer: Option C
Solution
Answer: Option C
Solution:
a + b = 5, ab = 3(a3 + b3) = (a + b)[(a + b)2 - 3ab]
= 5[52 - 3 × 3]
= 5(25 - 9)
= 80