Q. Find the 4 th term in the expansion of (2x−3)6 in simplest form.Answer:
Identify Variables: To find the 4th term in the expansion of (2x−3)6, 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,n−1)⋅am−n+1⋅bn−1, where C(m,n−1) is the binomial coefficient, which can be calculated as (m−n+1)!⋅(n−1)!m!.
Calculate Binomial Coefficient: First, we need to identify a, b, and m in our expression (2x−3)6. Here, a=2x, b=−3, and m=6.
Calculate a(m−n+1): Now, we calculate the 4th term, which means n=4. We need to find C(6,4−1) which is C(6,3). The binomial coefficient C(6,3) is calculated as 6!/[3!∗(6−3)!]=(6∗5∗4)/(3∗2∗1)=20.
Calculate b(n−1): Next, we calculate a(m−n+1) which is (2x)(6−4+1)=(2x)3. This equals 8x3.
Multiply Coefficients: Then, we calculate b(n−1) which is (−3)(4−1)=(−3)3=−27.
Final Result: Now, we multiply the binomial coefficient by the powers of 'a' and 'b' to get the 4th term: 20×8x3×(−27). This simplifies to 20×−216x3.
Final Result: Now, we multiply the binomial coefficient by the powers of 'a' and 'b' to get the 4th term: 20×8x3×(−27). This simplifies to 20×−216x3. Finally, we multiply 20 by −216 to get the coefficient of x3 in the 4th term: 20×−216=−4320. So, the 4th term is −4320x3.
More problems from Partial sums of geometric series