Folosind formula de inmultire a doua numere complexe scrise sub forma trigonometrica, obtinem:
[tex]...=\cos(\dfrac{\pi}{4}+\dfrac{3\pi}{4})+i\sin(\dfrac{\pi}{4}+\dfrac{3\pi}{4})=\cos\pi+i\sin\pi[/tex]
deci argumentul este [tex]\pi[/tex], iar modulul este [tex]\cos^2\pi+\sin^2\pi=1[/tex].
Formula de care vorbeam mai sus:
[tex]z_1=r_1(\cos x_1+i\sin x_1);\ z_2=r_2(\cos x_2+i\sin x_2)\Rightarrow[/tex][tex]\Rightarrow z_1\cdot z_2=r_1\cdot r_2[\cos(x_1+x_2)+i\sin(x_1+x_2)][/tex]
