Q. Find the 2 nd term in the expansion of (2x−9y)7 in simplest form.Answer:
Identify Binomial Expansion Form: Identify the general form of the binomial expansion.The binomial theorem states that (a+b)n expands to a sum of terms of the form C(n,k)⋅a(n−k)⋅bk, where C(n,k) is the binomial coefficient, equal to k!(n−k)!n!.
Determine Second Term: Determine the second term in the expansion.The second term corresponds to k=1, so we will calculate C(7,1)⋅(2x)7−1⋅(−9y)1.
Calculate Binomial Coefficient: Calculate the binomial coefficient C(7,1).C(7,1)=(1!(7−1)!)7!=(1!⋅6!)7!=17=7.
Calculate Powers: Calculate the powers of (2x) and (−9y).(2x)7−1=(2x)6 and (−9y)1=−9y.
Multiply Terms: Multiply the binomial coefficient by the powers of (2x) and (−9y). The second term is 7×(2x)6×(−9y)=7×64x6×(−9y)=−4032x6y.