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Find the 2nd term in the expansion of 
(x-6y)^(5) in simplest form.
Answer:

Find the 22nd term in the expansion of (x6y)5 (x-6 y)^{5} in simplest form.\newlineAnswer:

Full solution

Q. Find the 22nd term in the expansion of (x6y)5 (x-6 y)^{5} in simplest form.\newlineAnswer:
  1. Use Binomial Theorem: To find the 22nd term in the expansion of (x6y)5(x-6y)^{5}, we will use the binomial theorem. The general form of the kk-th term in the expansion of (a+b)n(a+b)^{n} is given by T(k)=C(n,k1)a(nk+1)b(k1)T(k) = C(n, k-1) \cdot a^{(n-k+1)} \cdot b^{(k-1)}, where C(n,k)C(n, k) is the binomial coefficient "nn choose kk". For the 22nd term, k=2k=2.
  2. Calculate Binomial Coefficient: We calculate the binomial coefficient for the 2nd2^{nd} term, which is C(5,21)=C(5,1)C(5, 2-1) = C(5, 1). The binomial coefficient C(n,k)C(n, k) is calculated as n!k!(nk)!\frac{n!}{k! \cdot (n-k)!}, where “!“\text{“!“} denotes factorial.
  3. Simplify Coefficient: C(5,1)C(5, 1) is calculated as 5!(1!(51)!)=5(14!)=5(124)=524\frac{5!}{(1! * (5-1)!)} = \frac{5}{(1 * 4!)} = \frac{5}{(1 * 24)} = \frac{5}{24}. Since 2424 is not a factor of 55, we simplify this to 55.
  4. Calculate Powers of a and b: Now we need to calculate the powers of aa and bb for the 22nd term. Since aa is xx and bb is 6y-6y, and we are looking for the 22nd term where k=2k=2, we have a52+1=x51=x4a^{5-2+1} = x^{5-1} = x^4 and b21=(6y)1=6yb^{2-1} = (-6y)^{1} = -6y.
  5. Multiply Coefficient and Powers: Multiplying the binomial coefficient by the powers of aa and bb, we get the 22nd term: T(2)=C(5,1)×x4×(6y)=5×x4×(6y)=30x4yT(2) = C(5, 1) \times x^4 \times (-6y) = 5 \times x^4 \times (-6y) = -30x^4y.

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