# If \cos 2v=- \frac 19 and v is acute, then

If $\mathrm{cos}2v=-\frac{19}{}$ and v is acute, then determine the value of v
I have tried using the double angle identity
$\mathrm{cos}2v={\mathrm{cos}}^{2}v-{\mathrm{sin}}^{2}v$
Ive
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rakije2v
Hint
Solving:
$\mathrm{cos}\left(2x\right)=-\frac{19}{}$
For the general case, let the R.H.S constant be k. Well