Question

- Cho tứ giác ABCD có : góc A = 120 độ , góc B = 90 độ , góc C = 2D . Tính C,D

Answer 1

Ta có: \(\widehat{A}+\widehat{B}+\widehat{C}+\widehat{D}=360^o\)

\(\Rightarrow120^o+90^o+\widehat{C}+\widehat{D}=360^o\)

\(\Rightarrow\widehat{C}+\widehat{D}=150^o\)

Lại có: \(\widehat{C}=2\widehat{D}\)

\(\Rightarrow2\widehat{D}+\widehat{D}=150^o\)

\(\Rightarrow3\widehat{D}=150^o\)

\(\Rightarrow\widehat{D}=50^o\)

\(\widehat{C}=\widehat{D}.2=50^o.2=100^o\)

Answer 2

Tứ giác có tổng số đo bốn góc là 360 độ

Suy ra \(\widehat{C}+\widehat{D}=360^o-\widehat{A}-\widehat{B}=180^o\)

Ta lại có \(\widehat{C}=2\widehat{D}\Rightarrow\widehat{C}-2\widehat{D}=0\)

Suy ra \(\widehat{C}=120^o,\widehat{D}=60^o\)