C3 trigonometry question help? Watch

MrScarecow901
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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.
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Kevin De Bruyne
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This seems to be a typical exam question - where part a helps you with part b. How far did you get with part a?
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brianeverit
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(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.
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JuniorXX
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60.98 and -60.98
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mattyd375
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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
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