<s>[INST] why $ \sin \theta = \frac{7}{8} \cos \theta$? I have an example:
$$ \tan \theta = \frac{\sin \theta}{\cos \theta} = \frac{7}{8} $$
and then this equation is true? why there is cos multiplied?:
$$ \sin \theta = \frac{7}{8} \cos \theta$$
 [/INST] You have $\dfrac{\sin \theta}{\cos \theta} = \dfrac{7}{8}$
Multiply both side by $\cos \theta$
You get $\dfrac{\sin \theta}{\cos \theta} \times\cos \theta = \dfrac{7}{8} \cos \theta$
So you get $\sin \theta = \dfrac78 \cos \theta$
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