Math Problem Statement

The coefficient of x^3 in the expansion of (2 + ax)^6 is 60. Find the two possible values of the constant a.

Solution

The image you uploaded shows a binomial expansion problem where you are asked to find the two possible values of the constant aa given that the coefficient of x3x^3 in the expansion of (2+ax)6(2 + a x)^6 is 60.

We can solve this problem using the binomial theorem. Let's break it down:

Step 1: General form of the binomial expansion

The binomial expansion of (2+ax)6(2 + ax)^6 can be written as:

(2+ax)6=k=06(6k)(2)6k(ax)k(2 + ax)^6 = \sum_{k=0}^{6} \binom{6}{k} (2)^{6-k} (a x)^k

The general term in this expansion is:

(6k)(2)6kakxk\binom{6}{k} (2)^{6-k} a^k x^k

Step 2: Finding the term for x3x^3

We need the term where k=3k = 3 because we are looking for the coefficient of x3x^3. For k=3k = 3, the term becomes:

(63)(2)63a3x3=(63)(2)3a3x3\binom{6}{3} (2)^{6-3} a^3 x^3 = \binom{6}{3} (2)^3 a^3 x^3

Step 3: Simplifying the expression

First, calculate (63)\binom{6}{3} and 232^3:

(63)=6×5×43×2×1=20\binom{6}{3} = \frac{6 \times 5 \times 4}{3 \times 2 \times 1} = 20

23=82^3 = 8

Thus, the term for x3x^3 is:

20×8×a3x3=160a3x320 \times 8 \times a^3 x^3 = 160 a^3 x^3

Step 4: Setting the coefficient equal to 60

You are told that the coefficient of x3x^3 is 60. Therefore, we set:

160a3=60160 a^3 = 60

Step 5: Solving for aa

Solve the equation 160a3=60160 a^3 = 60:

a3=60160=38a^3 = \frac{60}{160} = \frac{3}{8}

Now, take the cube root of both sides:

[ a = \sqrt[3]{\frac{3}{8}} = \frac{\sqrt[3]{3}}{\sqrt[3]{8}} = \frac{\sqrt[3]{3}}{2} ]

So, the two possible values for aa are:

[ a = \frac{\sqrt[3]{3}}{2} \quad \text{or} \quad a = -\frac{\sqrt[3]{3}}{2} ]

Conclusion:

The two possible values for aa are 332\frac{\sqrt[3]{3}}{2} and 332-\frac{\sqrt[3]{3}}{2}.


Would you like further details on the steps, or do you have any questions about this solution?

Here are some related questions:

  1. How do you generalize binomial expansions for other powers?
  2. Can the binomial theorem be applied to negative exponents?
  3. How do you find the coefficient of a general term in a binomial expansion?
  4. What is the significance of choosing the right value of kk in binomial expansions?
  5. How would the solution change if the exponent was different, say 7 instead of 6?

Tip: In binomial expansions, the power of xx in each term corresponds to the index kk. This can be used to directly identify which term to focus on for a given power of xx.

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Math Problem Analysis

Mathematical Concepts

Binomial Expansion
Algebra
Exponentiation
Cube Roots

Formulas

Binomial Theorem
Coefficient formula in binomial expansion

Theorems

Binomial Theorem

Suitable Grade Level

Grades 9-11