Q. Find the 3 rd term in the expansion of (x+5)7 in simplest form.Answer:
Use Binomial Theorem: To find the 3rd term in the expansion of (x+5)7, we will use the binomial theorem. The binomial theorem states that the nth term in the expansion of (a+b)m is given by the formula C(m,k−1)⋅am−k+1⋅bk−1, where C(m,k−1) is the binomial coefficient, which can be calculated as (m−k+1)!⋅(k−1)!m!. In this case, the 3rd term corresponds to k=3.
Calculate Binomial Coefficient: First, we calculate the binomial coefficient for the 3rd term, which is C(7,3−1)=C(7,2). This can be calculated as (7−2)!×2!7!=5!×2!7!=2×17×6=21.
Apply Binomial Theorem: Next, we apply the binomial theorem formula to find the 3rd term. We have a=x, b=5, m=7, and k=3. So the 3rd term is C(7,2)×x7−2×52=21×x5×25.
Simplify Expression: Now, we simplify the expression. Multiplying the binomial coefficient by the powers of x and 5, we get 21×x5×25=525×x5.
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