Choose the correct alternative answer

$a...be....a....beda.....ccd....bed.$

If $x^2+y^2=t+\frac{1}{t}$ and $x^4+y^4=t^2+\frac{1}{t^2}$,then $x^3 y \frac{d y}{d x}$ is equal to

Two point charges $+9e$ and $+e$ are placed at a distance of $16\, cm$ apart. Where should a third charge $q$ be placed between them so that it remains in equilibrium?

In India,electricity is supplied for domestic use at $220 \,V$. It is supplied at $110 \,V$ in the $USA$. If the resistance of a $60 \,W$ bulb for use in India is $R$,what will be the resistance of a $60 \,W$ bulb for use in the $USA$?

$A$ disc has mass $M$ and radius $R$. How much tangential force should be applied to the rim of the disc,so as to rotate with angular velocity $\omega$ in time $t$?

In Bryophytes,which stage produces haploid,autotrophic gametes?