Question

11. If X + c / x + 1 = c + 1, then x = (A)-1/c (B) C-2 (C) c-1/c (D) c-1/c+1
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Answer 1

Answer:

The given expression in for of sum can be written as

∑

r=0

n

(−1)

r

xyzC

r

+∑

r=0

n

(−1)

r

r(x+y+z)C

r

+∑

r=0

n

(−1)

r

r

2

(xy+yz+zx)C

r

−∑

r=0

n

(−1)

r

r

3

(xyz)C

r

Since n>3, the above terms form alternate positive and negative pairs thus cancelling each other and yielding zero.

Thus the final answer is 0.