Question

Cho tam giác ABC có góc A= 100; góc B- góc C= 50. Tính góc B và góc C

Answer 1

Ta có:\(\widehat{A}+\widehat{B}+\widehat{C}=180^o\)

\(\Rightarrow100^o+\widehat{B}+\widehat{C}=180^o\)

\(\Rightarrow\widehat{B}+\widehat{C}=80^o\)

Nên \(\left\{{}\begin{matrix}\widehat{B}-\widehat{C}=50^o\\\widehat{B}+\widehat{C}=80^o\end{matrix}\right.\)

\(\Rightarrow\left\{{}\begin{matrix}\widehat{B}+\widehat{C}+\widehat{B}-\widehat{C}=50^o+80^o\\\widehat{B}+\widehat{C}-\widehat{B}+\widehat{C}=80^o-50^o\end{matrix}\right.\)

\(\Rightarrow\left\{{}\begin{matrix}2\widehat{B}=130^o\\2\widehat{C}=30^o\end{matrix}\right.\)

\(\Rightarrow\left\{{}\begin{matrix}\widehat{B}=65^o\\\widehat{C}=15^o\end{matrix}\right.\)