[tex]tan\theta=\frac{sin\theta}{cos\theta}\\\\\\Look\ at\ the\ picture.\\\\In\ a\ right\ triangle:\\\\sin\theta=\frac{a}{c};\ cos\theta=\frac{b}{c};\ tan\theta=\frac{a}{b}\\\\\frac{sin\theta}{cos\theta}=\frac{\frac{a}{c}}{\frac{b}{c}}=\frac{a}{c}\times\frac{c}{b}=\frac{a}{b}=tan\theta[/tex]
