Math Problem Statement

Find the coefficient of x^3 in the expansion of (2-x)^5

Solution

To find the coefficient of x3x^3 in the expansion of (2x)5(2 - x)^5, we will use the Binomial Theorem, which states:

(a+b)n=k=0n(nk)ankbk(a + b)^n = \sum_{k=0}^{n} \binom{n}{k} a^{n-k} b^k

Here, a=2a = 2, b=xb = -x, and n=5n = 5. The general term in the binomial expansion is:

Tk=(nk)ankbkT_k = \binom{n}{k} a^{n-k} b^k

Substituting into the formula:

Tk=(5k)(2)5k(x)kT_k = \binom{5}{k} (2)^{5-k} (-x)^k

We are interested in the term that contains x3x^3. This means k=3k = 3, so we substitute k=3k = 3 into the general term:

T3=(53)(2)53(x)3T_3 = \binom{5}{3} (2)^{5-3} (-x)^3

Now, calculate each part:

(53)=5×42×1=10\binom{5}{3} = \frac{5 \times 4}{2 \times 1} = 10 (2)53=22=4(2)^{5-3} = 2^2 = 4 (x)3=x3(-x)^3 = -x^3

Now, combine these:

T3=10×4×(x3)=40x3T_3 = 10 \times 4 \times (-x^3) = -40x^3

Thus, the coefficient of x3x^3 is 40-40.

Would you like any further details or clarification?


Here are some related questions to explore:

  1. What is the general term in the binomial expansion of (ab)n(a - b)^n?
  2. How would you find the coefficient of x2x^2 in the same expansion?
  3. Can you find the constant term in the expansion of (2x)5(2 - x)^5?
  4. How does the sign of terms alternate in binomial expansions involving negative terms?
  5. How does Pascal's Triangle relate to binomial coefficients?

Tip: When expanding binomials, always check the signs of terms, especially when dealing with negative numbers!

Ask a new question for Free

By Image

Drop file here or Click Here to upload

Math Problem Analysis

Mathematical Concepts

Algebra
Binomial Expansion

Formulas

(a + b)^n = Σ( C(n, k) * a^(n-k) * b^k )
T_k = C(n, k) * a^(n-k) * b^k

Theorems

Binomial Theorem

Suitable Grade Level

Grades 9-12