Problem $09\mathrm{.}002-$ DEPENDENT MULTI$-$PART PROBLEM $-$ ASSIGN ALL PARTS

A current source in a linear circuit has $i_S=15cos(At+25)A.$

NOTE: This is a multi$-$part question. Once an answer is submitted, you will be unable to return to this part.

Problem $09\mathrm{.}002.$a $-$ Amplitude of a sinusoid

What is the amplitude of the current, where $A=21?$

The amplitude of the current is $$ A$.$