Question 2 of 20intermediate🔧 ApplyLong Answer4 marks

Expand each of the expressions in Exercises 1 to 5.

(2x−x2)5\left(\frac{2}{x} - \frac{x}{2}\right)^5
Correct Answer
32x5−40x3+20x−5x+5x38−x532\frac{32}{x^5} - \frac{40}{x^3} + \frac{20}{x} - 5x + \frac{5x^3}{8} - \frac{x^5}{32}
Exercise: EXERCISE 7.1 | Q: 2 | (Page 7)
For More Understanding

Explanation

This question is from Exercise 7.1, Question 2. The student needs to apply the binomial theorem for (a−b)n(a - b)^n expansion.

Using the formula:

(a−b)n=nC0⋅an−nC1⋅an−1⋅b+nC2⋅an−2⋅b2−⋯+(−1)n⋅nCn⋅bn(a - b)^n = {}^{n}C_0 \cdot a^n - {}^{n}C_1 \cdot a^{n-1} \cdot b + {}^{n}C_2 \cdot a^{n-2} \cdot b^2 - \cdots + (-1)^n \cdot {}^{n}C_n \cdot b^n

we substitute a=2xa = \frac{2}{x}, b=x2b = \frac{x}{2}, and n=5n = 5.

The binomial coefficients for n=5n = 5 are:

5C0=1,5C1=5,5C2=10,5C3=10,5C4=5,5C5=1{}^{5}C_0 = 1, \quad {}^{5}C_1 = 5, \quad {}^{5}C_2 = 10, \quad {}^{5}C_3 = 10, \quad {}^{5}C_4 = 5, \quad {}^{5}C_5 = 1

Each term requires careful simplification of powers of fractions.

Solution Steps

  1. Step 1: Apply binomial theorem for (a−b)n(a - b)^n where a=2xa = \frac{2}{x}, b=x2b = \frac{x}{2}, n=5n = 5

  2. Step 2: Write expansion:

    5C0⋅(2x)5−5C1⋅(2x)4⋅(x2)+5C2⋅(2x)3⋅(x2)2−5C3⋅(2x)2⋅(x2)3+5C4⋅(2x)⋅(x2)4−5C5⋅(x2)5{}^{5}C_0 \cdot \left(\frac{2}{x}\right)^5 - {}^{5}C_1 \cdot \left(\frac{2}{x}\right)^4 \cdot \left(\frac{x}{2}\right) + {}^{5}C_2 \cdot \left(\frac{2}{x}\right)^3 \cdot \left(\frac{x}{2}\right)^2 - {}^{5}C_3 \cdot \left(\frac{2}{x}\right)^2 \cdot \left(\frac{x}{2}\right)^3 + {}^{5}C_4 \cdot \left(\frac{2}{x}\right) \cdot \left(\frac{x}{2}\right)^4 - {}^{5}C_5 \cdot \left(\frac{x}{2}\right)^5
  3. Step 3: Substitute binomial coefficients:

    1⋅(2x)5−5⋅(2x)4⋅(x2)+10⋅(2x)3⋅(x2)2−10⋅(2x)2⋅(x2)3+5⋅(2x)⋅(x2)4−1⋅(x2)51 \cdot \left(\frac{2}{x}\right)^5 - 5 \cdot \left(\frac{2}{x}\right)^4 \cdot \left(\frac{x}{2}\right) + 10 \cdot \left(\frac{2}{x}\right)^3 \cdot \left(\frac{x}{2}\right)^2 - 10 \cdot \left(\frac{2}{x}\right)^2 \cdot \left(\frac{x}{2}\right)^3 + 5 \cdot \left(\frac{2}{x}\right) \cdot \left(\frac{x}{2}\right)^4 - 1 \cdot \left(\frac{x}{2}\right)^5
  4. Step 4: Simplify each term:

    32x5−40x3+20x−5x+5x38−x532\frac{32}{x^5} - \frac{40}{x^3} + \frac{20}{x} - 5x + \frac{5x^3}{8} - \frac{x^5}{32}