11cos^2(x)+8cos(x)−(9/11)=0
For 0

Question

11cos^2(x)+8cos(x)−(9/11)=0 
For 0 <= x <= 2pi

I've used the quadratic factorisation to get 
cos x =(1/11) and (-9/11)

there are supposed to be 3 answers but i can't seem to get them correctly

eliesaab · Answer

What you got are
$$
\cos(x) =\frac 1 {11}\
\cos(x)=-\frac 9{11}
$$

eliesaab · Answer

Are you here?

meowmers · Answer

Yes that is what i've got but the answer sheet says i'm supposed to find 3 values of (x)?

eliesaab · Answer

Use
$$
\cos( 2\pi -a) =\cos(a)
$$

meowmers · Answer

Sorry i don't understand you

likeabossssssss · Answer

$\bbox[5pt,midnightblue]{\LARGE\color{yellow}{\star ^\bigstar Welcome~to~~os~ ^\bigstar \star}}$

eliesaab · Answer

If a is a solution, then $ 2\pi -a $ is a also a solution

meowmers · Answer

I have tried 

$$\cos^{-1} \frac{ 1 }{ 11 } = 1.479rad$$  $$2pi-1.479$$

$$\cos^{-1} -\frac{ 9 }{ 11 } = 2.529rad$$ 

$$2pi-2.529$$

I'm not sure what's wrong anymore thanks for your help

eliesaab · Answer

So if 144 is a solution, then 360-144=216 is also a solution. So one solution can give you another one for free

eliesaab · Answer

360 - 1.479*180/pi=275 degrees

eliesaab · Answer

So you will have 2 solutions
84.74 degrees and 275 degrees