Math in Focus Trig Qs (1 Viewer)

[a1079atw]

Hi guys,

I've literally spent one hour on this type of question (acosx+bsinx = Rcos(x−α)) and still can't figure out the right answer...

May anyone please help me? I don't know where I did wrong. Here's my solution (didn't finish as I knew it's know the right answer)

Answer:

 

[QZP]

Hi, I had a quick inspection of your working out and I believe you dealt with the angles wrong. Also, you should put at the start of your solution "let ... = Rcos(x-a)" and then equate coefficients etc to find R and a otherwise it makes no sense :S

 

[funnytomato]

Hi, I had a quick inspection of your working out and I believe you dealt with the angles wrong. Also, you should put at the start of your solution "let ... = Rcos(x-a)" and then equate coefficients etc to find R and a otherwise it makes no sense :S

+1

also note cos(a+b)=cos(a)*cos(b)-sin(a)*sin(b)
and cos(a-b)=cos(a)*cos(b)+sin(a)*sin(b)