The angle between the straight lines $x^2+4xy+y^2=0$ is....... (in $^{\circ}$)

When a ceiling fan is switched on,it makes $10$ rotations in the first $3 \, s$. How many rotations will it make in the next $3 \, s$ (Assume uniform angular acceleration)?

If $f$ is a differentiable function such that $f(2x+1) = f(1-2x)$ for all $x \in R$,then find the minimum number of roots of the equation $f'(x) = 0$ in the interval $x \in (-5, 10)$,given that $f(2) = f(5) = f(10)$.

If $f: R \rightarrow C$ is defined by $f(x)=e^{2 i x}$ for $x \in R$, then $f$ is (where $C$ denotes the set of all complex numbers)

The technique used to make numerous copies of a specific segment of $DNA$ quickly and accurately is

Two thin lenses of focal lengths $f_1$ and $f_2$ are in contact and coaxial. The power of the combination is