Question Number 70296 by 7890542135678 last updated on 03/Oct/19
Commented by 7890542135678 last updated on 03/Oct/19
$${Find}\:\angle{BAC} \\ $$
Answered by mr W last updated on 03/Oct/19
Commented by mr W last updated on 03/Oct/19
$$\beta+\gamma+\mathrm{123}=\mathrm{180}\:\:\:...\left({i}\right) \\ $$$$\alpha+\left(\mathrm{15}+\beta\right)+\left(\mathrm{21}+\gamma\right)=\mathrm{180}\:\:\:...\left({ii}\right) \\ $$$$\left({ii}\right)−\left({i}\right): \\ $$$$\alpha+\mathrm{15}+\mathrm{21}−\mathrm{123}=\mathrm{0} \\ $$$$\Rightarrow\alpha=\mathrm{87}° \\ $$