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Find the 6th term in the expansion of 
(x+2y)^(8) in simplest form.
Answer:

Find the 66th term in the expansion of (x+2y)8 (x+2 y)^{8} in simplest form.\newlineAnswer:

Full solution

Q. Find the 66th term in the expansion of (x+2y)8 (x+2 y)^{8} in simplest form.\newlineAnswer:
  1. Use Binomial Theorem: To find the 6th6^{\text{th}} term in the expansion of (x+2y)8(x+2y)^{8}, 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,k)amkbkC(m, k) \cdot a^{m-k} \cdot b^k, where C(m,k)C(m, k) is the binomial coefficient "mm choose kk". For the 6th6^{\text{th}} term, kk will be (x+2y)8(x+2y)^{8}00 because the first term corresponds to (x+2y)8(x+2y)^{8}11.
  2. Calculate Binomial Coefficient: First, we need to calculate the binomial coefficient C(8,5)C(8, 5). This is equal to 8!5!×(85)!\frac{8!}{5! \times (8-5)!}, which simplifies to 8!5!×3!\frac{8!}{5! \times 3!}.
  3. Calculate Factorials: Calculating the factorial values, we get 8!=8×7×6×5!8! = 8 \times 7 \times 6 \times 5!, 5!=5×4×3×2×15! = 5 \times 4 \times 3 \times 2 \times 1, and 3!=3×2×13! = 3 \times 2 \times 1. Substituting these into the binomial coefficient formula, we have C(8,5)=8×7×63×2×1C(8, 5) = \frac{8 \times 7 \times 6}{3 \times 2 \times 1}.
  4. Calculate Binomial Coefficient: Simplifying the fraction, we get C(8,5)=8×7×63×2=56C(8, 5) = \frac{8 \times 7 \times 6}{3 \times 2} = 56.
  5. Calculate Remaining Term: Now we need to calculate the rest of the term, which is x(85)×(2y)5x^{(8-5)} \times (2y)^5. This simplifies to x3×(2y)5x^3 \times (2y)^5.
  6. Calculate Power of 22y: Raising 2y2y to the 55th power gives us 25×y52^5 \times y^5, which is 32×y532 \times y^5.
  7. Multiply Coefficients: Multiplying the binomial coefficient by the powers of xx and yy, we get the 66th term: 56×x3×32×y556 \times x^3 \times 32 \times y^5.
  8. Calculate Final Term: Finally, we multiply 5656 by 3232 to get the coefficient of the 66th term. This gives us 56×32=179256 \times 32 = 1792.
  9. Final Simplified Term: The 6th6^{th} term in the expansion of (x+2y)8(x+2y)^{8} in simplest form is therefore 1792×x3×y51792 \times x^3 \times y^5.

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