# How do you express the complex number in trigonometric form  3(cos 90° + i sin 90°)?

Your number, which is in trigonometric form, can be expressed in standard or rectangular form, $z = a + i b$, considering that:
cos(90°)=0
sin(90°)=1
$z = 3 \left(0 + 1 i\right) = 3 i$ a pure immaginary.