If $\log_e \left( \frac{a + b}{2} \right) = \frac{1}{2}(\log_e a + \log_e b)$,then the relation between $a$ and $b$ is:

$A$ transistor is used as a common emitter amplifier with a load resistance of $2 \ k\Omega$. The input resistance is $150 \ \Omega$. Base current is changed by $20 \ \mu A$,which results in a change in collector current by $1.5 \ mA$. The voltage gain of the amplifier is

$\int_0^\pi \frac{1}{1+\sin x} \, dx$ is equal to

$\int \sqrt{4 \cos ^2 x - 5 \sin ^2 x} \cos x \, dx =$

$A$ small source of sound moves on a circle as shown in the figure and an observer is standing at $O$. Let $n_1, n_2$ and $n_3$ be the frequencies heard when the source is at $A, B$ and $C$ respectively. Then

One litre of an aqueous solution contains $0.15 \ mol$ of $CH_3COOH$ $(pK_a = 4.8)$ and $0.15 \ mol$ of $CH_3COONa$. After the addition of $0.05 \ mol$ of solid $NaOH$ to this solution,the $pH$ will be