**f(x) = 2 in -2cos(3x)+1=2**

I know that it'll eventually turn out to be;

**cos(3x) = -1/2**but what should I do after this?

- Thread starter Karim
- Start date

I know that it'll eventually turn out to be;

- Joined
- Mar 16, 2016

- Messages
- 2,519

Do you mean "solve for x"?

Not sure what "solve for f(x)=2" means. Is f(x)=-2cos(3x)+1 ?

Not sure what "solve for f(x)=2" means. Is f(x)=-2cos(3x)+1 ?

- Joined
- Jun 18, 2007

- Messages
- 24,181

Please show us what you have tried andYes, I need to solve for x in the equation -2cos(3x)+1 = 2, without a calculator

Please follow the rules of posting in this forum, as enunciated at:

Please share your work/thoughts about this problem.

- Joined
- Jun 18, 2007

- Messages
- 24,181

Now time to use unit circle!View attachment 25418

It's part b which I'm stuck on, I already found the values of a, k and c and made the equation,f(x) = -2 cos(3x) + 1

View attachment 25419

Uptil now, I've made it till here. I just don't know how to simplify it further.

Cos (t) = -1/2

t = ? ............................

- Joined
- Mar 16, 2016

- Messages
- 2,519

So t = 2pi/3 +2k pi or 4pi/3 +2k pi where k is an integer.

But here t = 3x

So 3x = 2pi/3 + 2kpi or 4pi/3 + 2kpi

Divide both sides by 3

x = 2pi/9 +2kpi/3 or 4pi/9 + 2kpi/3

Now let k=0, 1, 2, etc until you pick up all the solutions between 0 and pi