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Find the 2 nd term in the expansion of 
(2x-9y)^(7) in simplest form.
Answer:

Find the 22 nd term in the expansion of (2x9y)7 (2 x-9 y)^{7} in simplest form.\newlineAnswer:

Full solution

Q. Find the 22 nd term in the expansion of (2x9y)7 (2 x-9 y)^{7} in simplest form.\newlineAnswer:
  1. Identify Binomial Expansion Form: Identify the general form of the binomial expansion.\newlineThe binomial theorem states that (a+b)n(a + b)^n expands to a sum of terms of the form C(n,k)a(nk)bkC(n, k) \cdot a^{(n-k)} \cdot b^k, where C(n,k)C(n, k) is the binomial coefficient, equal to n!k!(nk)!\frac{n!}{k!(n-k)!}.
  2. Determine Second Term: Determine the second term in the expansion.\newlineThe second term corresponds to k=1k = 1, so we will calculate C(7,1)(2x)71(9y)1C(7, 1) \cdot (2x)^{7-1} \cdot (-9y)^1.
  3. Calculate Binomial Coefficient: Calculate the binomial coefficient C(7,1)C(7, 1).C(7,1)=7!(1!(71)!)=7!(1!6!)=71=7C(7, 1) = \frac{7!}{(1!(7-1)!)} = \frac{7!}{(1! \cdot 6!)} = \frac{7}{1} = 7.
  4. Calculate Powers: Calculate the powers of (2x)(2x) and (9y)(-9y).(2x)71=(2x)6(2x)^{7-1} = (2x)^6 and (9y)1=9y(-9y)^1 = -9y.
  5. Multiply Terms: Multiply the binomial coefficient by the powers of (2x)(2x) and (9y)(-9y). The second term is 7×(2x)6×(9y)=7×64x6×(9y)=4032x6y7 \times (2x)^6 \times (-9y) = 7 \times 64x^6 \times (-9y) = -4032x^6y.

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