Question Number 49553 by ggny last updated on 07/Dec/18
Commented by mr W last updated on 07/Dec/18
$$\angle\mathrm{1}=\angle\mathrm{3} \\ $$$$\angle\mathrm{1}+\angle\mathrm{3}=\mathrm{90}° \\ $$$$\Rightarrow\mathrm{2}\angle\mathrm{1}=\mathrm{90}° \\ $$$$\Rightarrow\angle\mathrm{1}=\mathrm{45}° \\ $$$$\angle\mathrm{1}+\angle\mathrm{4}=\mathrm{180}° \\ $$$$\Rightarrow\angle\mathrm{4}=\mathrm{180}°−\angle\mathrm{1}=\mathrm{180}°−\mathrm{45}°=\mathrm{135}° \\ $$