MCQ
Let $f$ be a continuous function defined on $[0,1]$ such that $\int_0^1 f^2(x) d x=\left(\int_0^1 f(x) d x\right)^2$. Then, the range of $f$
- Ahas exactly two points
- Bhas more than two points
- Cis the interval $[0,1]$
- ✓is a singleton
We have,
$\int \limits_0^1 f^2(x) d x=\left(\int \limits_0^1 f(x) d x\right)^2, x \in[0,1]$
We know Cauchy Schwartz inequality
${\left[\int_a^b f(x) \cdot g(x) d x\right]^2 \leq \int_a^b(f(x))^2 d x }$
$\int_a^b(g(x))^2 d x$
Here, $g(x)=1$ and equality holds only when $\frac{f(x)}{g(x)}=\lambda$
So, $f(x)$ is constant function.
$\therefore f(x)$ is a singleton.
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