In the following sequence of reactions,the alkene affords the compound $B$:
$CH_3-CH=CH-CH_3$ $\xrightarrow{O_3} A$ $\xrightarrow{Zn, H_2O} B$
The compound $B$ is

$A$ speaker emits a sound wave of frequency $f_0$. When it moves towards a stationary observer with speed $u$,the observer measures a frequency $f_1$. If the speaker is stationary,and the observer moves towards it with speed $u$,the measured frequency is $f_2$. Then:

If $f(x) = (x^2 - 1)^7$,then $f^{(14)}(x)$ is equal to

Let $A, B$ and $C$ be three points in a plane. The locus of a point $P$ moving such that $PA^2 + PB^2 = 2PC^2$ is a

Which of the following statements is correct?

The magnifying power of a refracting type of astronomical telescope is $m$. If the focal length of the eyepiece is doubled,the magnifying power will become: