1. Understand the Property of Symmetric Limits
For any definite integral with symmetric limits [−a,a], we use the following property:
∫−aaϕ(x)dx=0 if ϕ(x) is an odd function.
A function ϕ(x) is odd if ϕ(−x)=−ϕ(x).
2. Define the Integrand
Let the entire function inside the integral be ϕ(x):
ϕ(x)=[f(x)+f(−x)][g(x)−g(−x)]
3. Test for Symmetry (Even or Odd)
To check if ϕ(x) is even or odd, we replace x with −x:
ϕ(−x)=[f(−x)+f(−(−x))][g(−x)−g(−(−x))]
ϕ(−x)=[f(−x)+f(x)][g(−x)−g(x)]
Now, observe the second bracket [g(−x)−g(x)]. We can factor out a negative sign:
[g(−x)−g(x)]=−[g(x)−g(−x)]
Substituting this back into our expression for ϕ(−x):
ϕ(−x)=[f(x)+f(−x)]⋅(−[g(x)−g(−x)])
ϕ(−x)=−[f(x)+f(−x)][g(x)−g(−x)]
4. Conclusion of the Integration
Since ϕ(−x)=−ϕ(x), the function ϕ(x) is an odd function.
According to the integral property for odd functions over symmetric limits:
Final Answer
The value of the integral is 0.
Correct Option: (d)