Question
If a + b = 5 and a^2 + b^2 = 13, find ab.
A. 6
B. -6
C. 12
D. -12
Answer: A. 6
Solution:
Given,
a + b = 5 and a^2 + b^2 = 13,
On squaring a + b = 5 both sides, we get
(a+b)2 = (5)2
⇒ a2 + b2 + 2ab = 25
⇒ 13 + 2ab = 25
⇒ 2ab = 25 − 13 = 12
⇒ ab = 12/2 = 6
∴ab = 6
Read More:
If x + (1/x) = 2, then what is the value of x^64 + x^121 = ?