Given that ,
(a) Find the exact value of
(b) solve the equation for 0< x < 180
Attempted solution
(a) 8cos^310 - 6cos10 = 2(cos3(10))
= 2cos30
=
(b) since 8cos^3x - 6cosx = 2cos 3x
2cos3x = -1
I cosine inversed but am not clear on what to do after that.
I know about the positive and negative quadrants.
However, the 3x is giving me some problems on adding and minus...
Note that 0< x <180
Hello PunchThanks for showing us your working so far. Your answer to (a) is perfect.
For (b), you're right so far. Note that if , then . Then you can say, since , we want to find all angles between and whose cosine is .
The first of these is , the next is , and so on. And these are the values of . So we get:(the last one being out of range.)Grandad