Explanation
Step -1: Identify binomial coefficients and number of terms in a binomial expansion.
(x2−x−2)5=(x2−2x+x−2)5
=(x(x−2)+1(x−2))5
=((x−2)(x+1))5
=(x−2)5(x+1)5
=[5C0x5+5C1x4.(−2)+5C2x3.(−2)2+5C3x2.(−2)3+5C4x.(−2)4+(−2)5]
×[5C0x5+5C1x4+5C2x3+5C3x2+5C4x+1]
∴coefficient of x5 in the expansion of the product (x−2)5(x+1)5
=−25+1+5C2.5C3(−2)3+5C3.5C2(−2)2+5C4.5C1(−2)1+5C1.5C4(−2)4
=−32+1−800+400−50+400
=−81
Hence, option C is correct.
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