+) \(\widehat{M}+\widehat{N}+\widehat{P}=180^o\) (định lý tổng 3 góc trong tam giác) mà\(\widehat{N}=2.\widehat{P}\)
\(=>\widehat{M}+2.\widehat{P}+\widehat{P}=180^o\)
\(=>2.\widehat{P}+\widehat{P}=180^o-\widehat{M}\)
\(=>3.\widehat{P}=180^o-90^o\)
\(=>3.\widehat{P}=90^o\)
\(=>\widehat{P}=\dfrac{90^o}{3}=30^o\)
+)\(\widehat{N}=2.\widehat{P}=>\widehat{N}=2.30^o=60^o\)