complex number stuffs (1 Viewer)

[synthesisFR]

could someone please help show me how to do these ( the ones in yellow) in a logical way? thank you so much!
i was trying doing them in my maths class today given as revision questions but couldnt figure them out...

 

[SadCeliac]

surely for 13c you can do difference of two squares over and over?? wait let me try

 

[SadCeliac]

Could you even just sub in z = [cis(theta)]^2 ???

 

[carrotsss]

First one, can do the rest tomorrow if u need

 

[synthesisFR]

Could you even just sub in z = [cis(theta)]^2 ???

the solution he wrote was subbing in z = (cos2(theta)-1)/2


but it makes more sense to sub in sin^2theta instead

ik its the same but like skipping that one step confsued me so much rip

 

[synthesisFR]

Could you explain 15a please. I got lost after they started doing cis2a