I=∫04g(x)f(x)dxFrom the given equation,
g(x)=f(x)+f(4−x)Using the property
∫0ah(x)dx=∫0ah(a−x)dx:
I=∫04g(4−x)f(4−x)dxSince
g(4−x)=f(4−x)+f(x)=g(x):
I=∫04g(x)f(4−x)dxAdding the two equations for
I:
2I=∫04g(x)f(x)+f(4−x)dx2I=∫04g(x)g(x)dx=∫041dx2I=4⇒I=2Answer:
2