a2+2ab-2b-1 কোনটি?
A
(a-b)(a+2b+1)
B
(a+1)(a+2b+1)
C
(a+1)(a+2b-1)
D
(a-1)(a-2b-1)
Correct Answer: (a-b)(a+2b+1)
দেয়া আছে, a2 + 2ab - 2b - 1 = a2 + 2ab + b2 - b2 - 2b - 1 = (a + b)2 = (b2 + 2×b×1 + 1)2 = (a + b)2 – (b + 1)2 = (a + b + b + 1) {(a + b − (b + 1)} = (a + 2b + 1) (a + b - b −1) = (a + 2b + 1) (a - 1) = (a – 1) (a + 2b + 1)