DavidH can't remember how to...

Arh, I can't for the life of me remember how to solve this equation for complex z:
z⁴ = -1

I remember you can write z = a + ib, substitute for z and the compare the real and imaginary parts blahblahblah but that takes aaages. There's definitely a quicker way (did it involve De Moivre's Theorem?)

Flip, flip and double flip! I handed in my old textboooks so I can't check in them and I start uni next week!

Anyone? Pleeease?! :(

Ah, found the answer. It was De Moivre and it was here all along.