Evaluate ( + )^6 - ( - )^6.
396
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
Step 1: Apply binomial theorem to expand both expressions.
( + )⁶ = ⁶C₀()⁶ + ⁶C₁()⁵() + ⁶C₂()⁴()² + ⁶C₃()³()³ + ⁶C₄()²()⁴ + ⁶C₅()()⁵ + ⁶C₆()⁶
( - )⁶ = ⁶C₀()⁶ - ⁶C₁()⁵() + ⁶C₂()⁴()² - ⁶C₃()³()³ + ⁶C₄()²()⁴ - ⁶C₅()()⁵ + ⁶C₆()⁶
Step 2: Subtract the two expansions.
When subtracting, terms with even powers of cancel out, and terms with odd powers of double.
( + )⁶ - ( - )⁶ = 2[⁶C₁()⁵() + ⁶C₃()³()³ + ⁶C₅()()⁵]
Step 3: Calculate the binomial coefficients and simplify each term.
⁶C₁ = 6, ⁶C₃ = 20, ⁶C₅ = 6
⁶C₁()⁵() = $$6 \times 9$$$\sqrt{3}\sqrt{2}\sqrt{6}$
⁶C₃()³()³ = √$$3 \times 2$$$\sqrt{2}\sqrt{6}$
⁶C₅()()⁵ = 6 × √$$3 \times 4$$$\sqrt{2}\sqrt{6}$
Step 4: Add all terms and multiply by 2.
= 2[54 + 120 + 24]
= 2[198]
= 396