Converting to a+jb form

I'm having problems with this, the annoying thing is I've done it, however I can't remember how I did the previous example or I have changed the mode on my calculator and it's destroyed what I was doing.

I have to convert this;

2.4 /_ -(π/6)

So I have;

a= r cos ϴ = 2.4 cos -30 = ???

b= r sin ϴ = 2.4 sin -30 = ???

I input it into my casio and just comes up with maths error, I changed my calculator to radians and then back and now I don't know why I can't do this.

So if someone could walk me through it would be great, cheers.

I don't know that that is...



You should really know off the top of your head that cos(-30) = sqrt(3)/2 and sin(-30) = -1/2.

Anywho, if you're sure you're in degree mode then trying doing 2.4 sin (-30), i.e: explicitly use the bracket

I have no idea what's gone wrong, tried it on my work's calculator and it works fine. I've clearly changed something in the calculator and it's not working.