Q. Find the 5th term in the expansion of (5x−y)6 in simplest form.Answer:
Identify general term: Identify the general term of a binomial expansion.The general term in the expansion of (a−b)n is given by T(k+1)=C(n,k)⋅a(n−k)⋅bk, where C(n,k) is the binomial coefficient "n choose k".
Determine specific term: Determine the specific term we are looking for.We want to find the 5th term, which corresponds to k=4, since the first term corresponds to k=0.
Apply binomial theorem: Apply the binomial theorem to find the 5th term. Using the formula from Step 1, we substitute n=6 and k=4 to find T(5)=C(6,4)⋅(5x)6−4⋅(−y)4.
Calculate binomial coefficient: Calculate the binomial coefficient C(6,4).C(6,4)=4!⋅(6−4)!6!=((4⋅3⋅2⋅1)⋅(2⋅1))(6⋅5⋅4⋅3⋅2⋅1)=(2⋅1)(6⋅5)=15.
Substitute values: Substitute the values into the term.T(5)=15×(5x)2×(−y)4=15×25x2×y4.
Simplify term: Simplify the term. T(5)=15×25×x2×y4=375×x2×y4.
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