Question

Cho tam giác ABC có A=70o , B-C=20o. Tính B và C.

Answer 1

ta có : \(\widehat{B}-\widehat{C}=20^o\Rightarrow\widehat{B}=20^o+\widehat{C}\)

ta có tam giác ABC bằng \(180^o\) có \(\widehat{A}=70^o\)

\(\Rightarrow\widehat{B}+\widehat{C}=180^o-\widehat{A}=180^o-70^o=110^o\)

\(\Leftrightarrow20^o+\widehat{C}+\widehat{C}=110^o\Leftrightarrow2\widehat{C}=110^o-20^o=90^o\)

\(\Leftrightarrow\widehat{C}=\dfrac{90}{2}=45^o\)

ta có \(\widehat{C}=45^o\Rightarrow\widehat{B}=20^o+\widehat{C}=20^o+45^o=65^o\)

vậy \(\widehat{B}=65^ovà\widehat{C}=45^o\)