Product of any r consecutive natural numbers is always divisible by
r!
(r + 4)!
(r + 1)!
(r + 2)!
If C0, C1, C2, ..., Cn denote the coefficients in the expansion of (1 + x)n, then the value of C1 + 2C2 + 3C3 + ... + nCn is
n . 2n - 1
(n + 1)2n - 1
(n + 1)2n
(n + 2)2n - 1
The angle between the lines joining the foci of an ellipse to one particular extremity of the minor axis is 90°. The eccentricity of the ellipse is
1/8
1/√3
√(2/3)
√(1/2)
For each n N, 23n - 1is divisible by
7
8
6
16
A.
7
Hence, it is divisible by 7.