Ectophloic siphonostele is found in

$NPN$ transistors are preferred to $PNP$ transistors because they have

If $|x| < 1$,then the sum of the series $1 + 2x + 3x^2 + 4x^3 + \dots \infty$ will be

If $\left|\begin{array}{ccc}x & x^2 & 1+x^3 \\ y & y^2 & 1+y^3 \\ z & z^2 & 1+z^3\end{array}\right|=0$ and $x \neq y \neq z$,then $1+x y z$ is equal to

If in a $\triangle ABC$,$\frac{1}{a+c} + \frac{1}{b+c} = \frac{3}{a+b+c}$,then $\angle C$ is equal to (in $^{\circ}$)

The condition that $f(x)=a x^3+b x^2+c x+d$ has no extreme value,is