$4\mathrm{.}5-4$ Over an interval $|$t$|1,$ an angle$-$modulated signal is given by

$$EM $($t$)=10$ cos $(13,000$t $+0\mathrm{.}3$$)$

It is known that the carrier frequency c $=12,000$$.$

$($a$)$ Assuming the modulated signal is a PM signal with kp $=1000,$ determine m$($t$)$ over the

interval $|$t$|1.$

$($b$)$ Assuming the modulated signal is an FM signal with kf$=1000,$ determine m$($t$)$ over the

interval $|$t$|1.$

$,$ kf$=104$$,$ and kp $=25$$.$