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
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A- 2
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B- 1
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C0
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D1
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.**