Question

6cos^2 theta-cos theta-1=0

solve for theta in degrees​

Answer 1

`6\cos^2(\theta )-\cos(\theta )-1=0\hspace{5em}\stackrel{\textit{let's just for a second make}}{\cos(\theta )=Z} \\\\\\ 6Z^2-Z-1\implies (3Z+1)(2Z-1)=0\implies [3\cos(\theta )+1][2\cos(\theta )-1]=0 \\\\[-0.35em] ~\dotfill`

`3\cos(\theta )+1=0\implies 3\cos(\theta )=-1\implies \cos(\theta )=-\cfrac{1}{3} \\\\\\ \theta =\cos^(-1)\left(-\cfrac{1}{3} \right)\implies \theta \approx \begin{cases} 109.47^o\\ 250.53^o \end{cases} \\\\[-0.35em] ~\dotfill\\\\ 2\cos(\theta )-1=0\implies 2\cos(\theta )=1\implies \cos(\theta )=\cfrac{1}{2} \\\\\\ \theta =\cos\left( \cfrac{1}{2} \right)\implies \theta = \begin{cases} 60^o\\ 300^o \end{cases}`

Make sure your calculator is in Degree mode.