[tex]\frac{dy}{dx}[/tex] = tanxtany
differentiate 6cosxsiny using the ' product rule '
6[ cosxcosy[tex]\frac{dy}{dx}[/tex] + siny( - sinx )] = 0
6[ cosxcosy [tex]\frac{dy}{dx}[/tex] - sinxsiny ] = 0
cosxcosy [tex]\frac{dy}{dx}[/tex] = sinxsiny
[tex]\frac{dy}{dx}[/tex] = [tex]\frac{sinxsiny}{cosxcosy}[/tex] = tanxtany
