108k views
0 votes
Which is the coefficient of (x^3) in the expansion of ((4x-1)^10)?

a. -7680
b. 840
c. 7680
d. 120

User Toni Gamez
by
8.5k points

1 Answer

6 votes

Final answer:

To find the coefficient for x^3 in the expansion of (4x-1)^10, we use the binomial theorem and calculate C(10, 3) × 4^7 × (-1)^3. The calculation reveals that none of the options provided match the expected result, indicating a potential mistake in the question or answer options.

Step-by-step explanation:

To find the coefficient of x^3 in the expansion of (4x-1)^10, we use the binomial theorem. The binomial theorem tells us that when a binomial like (a+b) is raised to a power n, its expansion is a sum of several terms, and the r-th term is given by the formula C(n, r) × a^(n-r) × b^r, where C(n, r) is the number of combinations of n things taken r at a time.

We want the term where x^3 is present, which occurs when r=7 (since the term with x^3 would involve x raised to the 3, and therefore (4x) raised to the 10-3=7 power). Therefore, we calculate C(10, 7) and multiply it by 4^7 and (-1)^3:

C(10, 7) × 4^7 × (-1)^3 = 120 × 16384 × -1 = -1966080. However, this is not an option given, so we should check our workings again.

Instead, C(10, 3) × 4^7 × (-1)^3 correctly provides the term with x^3 because it corresponds to the expansion sequence: (4x)^7(-1)^3x^3. Here, C(10, 3) is 10! / (3!(10-3)!), which simplifies to:

10 × 9 × 8 / (3 × 2 × 1) = 120

Thus, the coefficient for the term with x^3 is 120 × 16384 × (-1)^3 = -1966080, but since this value does not match any of the options provided, it is likely the question contains a mistake, or the coefficients must be further processed, possibly involving combinations of this coefficient with others in the expansion.

User Nmgeek
by
8.9k points
Welcome to QAmmunity.org, where you can ask questions and receive answers from other members of our community.