(a+b) = 7 এবং (a-b) = 5 হলে ab=কত?

A 6

B 5

C 7

D 4

Correct Answer: Option A

দেওয়া আছে,
(a+b) = 7
এবং (a-b) = 5
∴ab = (a+b/2)² - (a-b/2)²=(7/2)² - (5/2)²
=49/4 - 25/4
=49-25/4
=24/4
=6