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Find the 3 rd term in the expansion of 
(x+5)^(7) in simplest form.
Answer:

Find the 33 rd term in the expansion of (x+5)7 (x+5)^{7} in simplest form.\newlineAnswer:

Full solution

Q. Find the 33 rd term in the expansion of (x+5)7 (x+5)^{7} in simplest form.\newlineAnswer:
  1. Use Binomial Theorem: To find the 3rd3^{\text{rd}} term in the expansion of (x+5)7(x+5)^{7}, we will use the binomial theorem. The binomial theorem states that the nthn^{\text{th}} term in the expansion of (a+b)m(a+b)^{m} is given by the formula C(m,k1)amk+1bk1C(m, k-1) \cdot a^{m-k+1} \cdot b^{k-1}, where C(m,k1)C(m, k-1) is the binomial coefficient, which can be calculated as m!(mk+1)!(k1)!\frac{m!}{(m-k+1)! \cdot (k-1)!}. In this case, the 3rd3^{\text{rd}} term corresponds to k=3k=3.
  2. Calculate Binomial Coefficient: First, we calculate the binomial coefficient for the 33rd term, which is C(7,31)=C(7,2)C(7, 3-1) = C(7, 2). This can be calculated as 7!(72)!×2!=7!5!×2!=7×62×1=21\frac{7!}{(7-2)! \times 2!} = \frac{7!}{5! \times 2!} = \frac{7 \times 6}{2 \times 1} = 21.
  3. Apply Binomial Theorem: Next, we apply the binomial theorem formula to find the 33rd term. We have a=xa = x, b=5b = 5, m=7m = 7, and k=3k = 3. So the 33rd term is C(7,2)×x72×52=21×x5×25C(7, 2) \times x^{7-2} \times 5^{2} = 21 \times x^{5} \times 25.
  4. Simplify Expression: Now, we simplify the expression. Multiplying the binomial coefficient by the powers of xx and 55, we get 21×x5×25=525×x521 \times x^{5} \times 25 = 525 \times x^{5}.

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