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Find the fourth term of the binomial expansion of \((x - k)^...

Find the fourth term of the binomial expansion of (xk)5 in descending powers of x.<

A.

10x3k2

B.

5x3k2

C.

5x2k3

D.

10x2k3

Correct answer is D

(xk)5=5C0x5(k)0+5C1x4(k)1+...

The fourth term in the expansion = ^{5}C_{4 - 1}(x)^{5 - 3}(-k)^{3 = 10 \times x^{2} \times -k^{3}

= 10x2k3