$\frac{1}{1 + x^{(b-a)} + x^{(c-a)}} + \frac{1}{1 + x^{(a-b)} + x^{(c-b)}} + \frac{1}{1 + x^{(b-c)} + x^{(a-c)}} =$ $x$
Aptitude
Surds and Indices
Difficulty: Hard
Choose an option
-
A0
-
B1
-
C$x^{a-b-c}$
-
DNone of these
Answer
Correct Answer: 1
Explanation
Concept & Logic
This question tests your ability to manipulate negative exponents and find a common denominator across cyclic fractions.
The fundamental rule of negative exponents states:
$$x^{-n} = \frac{1}{x^n}$$
In this expression, we can rewrite terms like $x^{(b-a)}$ as $\frac{x^b}{x^a}$. Multiplying the numerator and denominator of each fraction by the denominator's hidden base will normalize all three fractions to share the exact same common denominator.
Step-by-step Solution
Let's handle the three main fractional terms one by one.
For the first term:
$$\frac{1}{1 + \frac{x^b}{x^a} + \frac{x^c}{x^a}}$$
Multiply the numerator and the denominator by $x^a$:
$$\frac{x^a}{x^a(1) + x^a(\frac{x^b}{x^a}) + x^a(\frac{x^c}{x^a})} = \frac{x^a}{x^a + x^b + x^c}$$
For the second term:
$$\frac{1}{1 + \frac{x^a}{x^b} + \frac{x^c}{x^b}}$$
Multiply the numerator and the denominator by $x^b$:
$$\frac{x^b}{x^b + x^a + x^c}$$
For the third term:
$$\frac{1}{1 + \frac{x^b}{x^c} + \frac{x^a}{x^c}}$$
Multiply the numerator and the denominator by $x^c$:
$$\frac{x^c}{x^c + x^b + x^a}$$
Now, add the three simplified fractions together. Since all three have the exact same denominator $(x^a + x^b + x^c)$, you can simply add their numerators:
$$\frac{x^a + x^b + x^c}{x^a + x^b + x^c}$$
Any non-zero expression divided by itself equals $1$.
Exam Strategy & Shortcut
**Symmetry & Value Putting**: This expression is perfectly symmetrical concerning $a$, $b$, and $c$. For any such generalized cyclic expression where the options are constants (like 0 and 1), assume simple identical values for the variables.
Let $a = 1$, $b = 1$, $c = 1$.
The expression becomes:
$\frac{1}{1 + x^0 + x^0} + \frac{1}{1 + x^0 + x^0} + \frac{1}{1 + x^0 + x^0}$
Since $x^0 = 1$, this turns into $\frac{1}{1+1+1} + \frac{1}{1+1+1} + \frac{1}{1+1+1} = \frac{1}{3} + \frac{1}{3} + \frac{1}{3} = 1$.
Common Pitfall
Students often waste time trying to find the Least Common Multiple (LCM) of the massive original denominators without simplifying the negative exponents first. This leads to a horrific algebraic mess that consumes too much time.
Final Answer
**Therefore, the correct answer is 1.**