Question 16 of 20intermediate🔧 ApplyNumerical4 marks

Evaluate (3\sqrt{3} + 2\sqrt{2})^6 - (3\sqrt{3} - 2\sqrt{2})^6.

Correct Answer

3966\sqrt{6}

Exercise: Miscellaneous Exercise on Chapter 7 | Q: 2 | (Page 8)
For More Understanding

Explanation

This question from the Miscellaneous Exercise on Chapter 7 requires applying the binomial theorem to evaluate the difference of two sixth powers. The key insight is recognizing that when we subtract (a-b)^n from (a+b)^n, the terms with even powers of b cancel out, while terms with odd powers of b double. This pattern is similar to Question 11 in the textbook which asks for (a+b)^4 - (a-b)^4.

Solution Steps

  1. Step 1: Apply binomial theorem to expand both expressions.

    (3\sqrt{3} + 2\sqrt{2})⁶ = ⁶C₀(3\sqrt{3})⁶ + ⁶C₁(3\sqrt{3})⁵(2\sqrt{2}) + ⁶C₂(3\sqrt{3})⁴(2\sqrt{2})² + ⁶C₃(3\sqrt{3})³(2\sqrt{2})³ + ⁶C₄(3\sqrt{3})²(2\sqrt{2})⁴ + ⁶C₅(3\sqrt{3})(2\sqrt{2})⁵ + ⁶C₆(2\sqrt{2})⁶

    (3\sqrt{3} - 2\sqrt{2})⁶ = ⁶C₀(3\sqrt{3})⁶ - ⁶C₁(3\sqrt{3})⁵(2\sqrt{2}) + ⁶C₂(3\sqrt{3})⁴(2\sqrt{2})² - ⁶C₃(3\sqrt{3})³(2\sqrt{2})³ + ⁶C₄(3\sqrt{3})²(2\sqrt{2})⁴ - ⁶C₅(3\sqrt{3})(2\sqrt{2})⁵ + ⁶C₆(2\sqrt{2})⁶

  2. Step 2: Subtract the two expansions.

    When subtracting, terms with even powers of 2\sqrt{2} cancel out, and terms with odd powers of 2\sqrt{2} double.

    (3\sqrt{3} + 2\sqrt{2})⁶ - (3\sqrt{3} - 2\sqrt{2})⁶ = 2[⁶C₁(3\sqrt{3})⁵(2\sqrt{2}) + ⁶C₃(3\sqrt{3})³(2\sqrt{2})³ + ⁶C₅(3\sqrt{3})(2\sqrt{2})⁵]

  3. Step 3: Calculate the binomial coefficients and simplify each term.

    ⁶C₁ = 6, ⁶C₃ = 20, ⁶C₅ = 6

    ⁶C₁(3\sqrt{3})⁵(2\sqrt{2}) = $$6 \times 9$$$\sqrt{3}××\sqrt{2}=54 = 54\sqrt{6}$

    ⁶C₃(3\sqrt{3})³(2\sqrt{2})³ = 20×320 \times 3√$$3 \times 2$$$\sqrt{2}=120 = 120\sqrt{6}$

    ⁶C₅(3\sqrt{3})(2\sqrt{2})⁵ = 6 × √$$3 \times 4$$$\sqrt{2}=24 = 24\sqrt{6}$

  4. Step 4: Add all terms and multiply by 2.

    = 2[546\sqrt{6} + 1206\sqrt{6} + 246\sqrt{6}]

    = 2[1986\sqrt{6}]

    = 3966\sqrt{6}