MCQ
If $f(x)$ is a continuous periodic function with period $T,$ then the integral $I = \int_a^{a + T} {f(x)\,dx} $ is
  • A
    Equal to $2a$
  • B
    Equal to $3a$
  • Independent of $a$
  • D
    None of these

Answer

Correct option: C.
Independent of $a$
c
(c) Consider the function $g(a) = \int_a^{a + T} {f(x)dx} $

$ = \int_a^0 {f(x)dx + \int_0^T {f(x)dx + \int_T^{a + T} {\,\,f(x)dx} } } $

Putting $x - T = y$ in last integral, we get

$\int_T^{a + T} {f(x)dx = \int_0^a {f(y + T)dy = \int_0^a {f(y)dy} } } $

==> $g(a) = \int_a^0 {f(x)dx + \int_0^1 {f(x)dx + \int_0^a {f(x)dx} } } $$ = \int_0^T {f(x)dx} $

Hence $ g(a)$  is independent of  $a.$

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