Q. Find the 2nd term in the expansion of (2x−5y)5 in simplest form.Answer:
Use Binomial Theorem: To find the 2nd term in the expansion of (2x−5y)5, we will use the binomial theorem. The general form of the k-th term in the expansion of (a+b)n is given by T(k)=C(n,k−1)⋅an−k+1⋅bk−1, where C(n,k) is the binomial coefficient "n choose k". For the 2nd term, k=2.
Calculate Binomial Coefficient: First, we calculate the binomial coefficient for the 2nd term, which is C(5,2−1)=C(5,1). The binomial coefficient C(n,k) is calculated as k!⋅(n−k)!n!, where “!“ denotes factorial.
Calculate Powers of a and b: Calculating C(5,1) gives us 1!∗(5−1)!5!=1∗4!5=1∗245=245. Since 24 is the factorial of 4, we simplify it to get 245=5.
Multiply Coefficient and Powers: Now we need to calculate the powers of a and b for the 2nd term. Since a=2x and b=−5y, and we are looking for the 2nd term where k=2, we have a5−2+1=a4 and b2−1=b1.
Simplify the Expression: Calculating the powers, we get (2x)4=16x4 and (−5y)1=−5y.
Simplify the Expression: Calculating the powers, we get (2x)4=16x4 and (−5y)1=−5y.Multiplying the binomial coefficient by the powers of a and b, we get the 2nd term: T(2)=C(5,1)⋅(2x)4⋅(−5y)1=5⋅16x4⋅−5y.
Simplify the Expression: Calculating the powers, we get (2x)4=16x4 and (−5y)1=−5y.Multiplying the binomial coefficient by the powers of a and b, we get the 2nd term: T(2)=C(5,1)⋅(2x)4⋅(−5y)1=5⋅16x4⋅−5y.Simplifying the expression, we get T(2)=5⋅16⋅−5⋅x4⋅y=−400⋅x4⋅y.
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