Question Number 76713 by peter frank last updated on 29/Dec/19
$${If}\:\mathrm{cos}\:{y}={x}\mathrm{cos}\:\left({a}+{y}\right),{show} \\ $$$${that}\:\frac{{dy}}{{dx}}=\frac{\mathrm{cos}\:^{\mathrm{2}} \left({a}+{y}\right)}{\mathrm{sin}\:{a}} \\ $$