Ok this is a negative number.
All negative numbers have argument [tex]\pi[/tex]
Obviously, the module of this number is [tex]\vert-4\vert=4[/tex]
The general trigonometric form of a complex number is:
[tex]z=\vert z\vert(cos\theta+i\sin\theta)[/tex]
We deduce the trigonometric for of -4:
[tex]-4=4(cos\pi+i\sin\pi)[/tex]
