# C3 trigonometry question help?Watch

#1
I need some help with this question, mainly the second question can someone tell me what they get and how?

Express 4cosx - sinx in the form Rcos(x+a), where R>0, and 0<a<90.

Hence solve the equation 4cosx - sinx=2, giving all solutions, for which -180<x<180.
0
4 years ago
#2
This seems to be a typical exam question - where part a helps you with part b. How far did you get with part a?
0
4 years ago
#3
(Original post by MrScarecow901)
I need some help with this question, mainly the second question can someone tell me what they get and how?

Express 4cosx - sinx in the form Rcos(x+a), where R>0, and 0<a<90.

Hence solve the equation 4cosx - sinx=2, giving all solutions, for which -180<x<180.
expand Rcos(x+a) using the addition theorem then compare with 4cos x-sin x to find the values of R and a.
0
3 years ago
#4
60.98 and -60.98
0
3 years ago
#5
so for part (a) i got root17cos(x+14.04)
for part (b) put this equal to 2 and then shouldnt be too hard to solve from there rearranging to get cos(x+14.04)=2/root17 and thats a c2 question so should be easy from there
0
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