More Questions from Surds and Indices

If $a + b + c = 0$, then the value of $(x^a)^{a^2-bc} \cdot (x^b)^{b^2-ca} \cdot (x^c)^{c^2-ab}$ is equal to

Aptitude Surds and Indices Difficulty: Medium
Choose an option
  • A
    - 2
  • B
    - 1
  • C
    0
  • D
    1

Answer

Correct Answer: 1

Explanation

Concept & Formula This problem combines the fundamental laws of exponents with a core algebraic identity. The exponent rules we need are: $$(x^m)^n = x^{mn}$$ $$x^m \cdot x^n = x^{m+n}$$ The standard algebraic identity for cubes is: $$a^3 + b^3 + c^3 - 3abc = (a+b+c)(a^2+b^2+c^2-ab-bc-ca)$$ A crucial deduction from this identity is that if $a+b+c=0$, then $a^3+b^3+c^3 = 3abc$. Step-by-step Solution First, simplify each term in the product by multiplying the inner and outer exponents: 1. First term: $(x^a)^{a^2-bc} = x^{a(a^2-bc)} = x^{a^3-abc}$ 2. Second term: $(x^b)^{b^2-ca} = x^{b(b^2-ca)} = x^{b^3-abc}$ 3. Third term: $(x^c)^{c^2-ab} = x^{c(c^2-ab)} = x^{c^3-abc}$ Next, multiply these three terms together by adding their exponents: $$x^{(a^3-abc) + (b^3-abc) + (c^3-abc)}$$ Group the similar terms in the exponent: $$x^{a^3 + b^3 + c^3 - 3abc}$$ We are given that $a + b + c = 0$. According to the algebraic identity, this means $a^3 + b^3 + c^3 - 3abc = 0$. Substitute $0$ into the exponent: $$x^0 = 1$$ Exam Strategy & Shortcut **Value Assumption Method**: Whenever you are given a conditional equation like $a+b+c=0$ and asked to find the value of a generalized expression, pick simple integers that satisfy the condition. Let $a = 1$, $b = -1$, and $c = 0$. Substitute these into the given expression: $(x^1)^{1^2-0} \cdot (x^{-1})^{(-1)^2-0} \cdot (x^0)^{0^2-(-1)} = x^1 \cdot x^{-1} \cdot 1 = x^0 = 1$. This bypasses all complex algebra and gives you the answer in seconds. Common Pitfall A major trap is incorrectly expanding $a(a^2-bc)$ as $a^3-c$, completely missing the $b$ variable, or forgetting the negative signs when adding the exponents together. Always write out your expansions clearly before combining them. Final Answer **Therefore, the correct answer is 1.**
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