Đáp án:
a) $b\perp AB$
b) $\widehat{BDC}=60^{0}$
c) $\widehat{BIC}= 120^{0}$
Giải thích các bước giải:
a) Ta có: $\widehat{CAB}+\widehat{DBA}=180^{0}$ (trong cùng phía)
$\rightarrow \widehat{DBA}=180^{0}-\widehat{CAB}$
$\rightarrow \widehat{DBA}=180^{0}-90^{0}=90^{0}$
$\rightarrow b\perp AB$
b) Ta có: $\widehat{ACD}+\widehat{BDC}=180^{0}$ (trong cùng phía)
$\rightarrow \widehat{BDC}=180^{0}-\widehat{ACD}$
$\rightarrow \widehat{BDC}=180^{0}-120^{0}=60^{0}$
c) Vì Cx tia phân giác của $\widehat{ACD}$ (gt)
$\rightarrow \widehat{ACx}=\widehat{DCx}=\dfrac{\widehat{ACD}}{2}=\dfrac{120^{0}}{2}=60^{0} $
Ta có: $\widehat{ACx}+\widehat{BIC}=180^{0}$ (trong cùng phía)
$\rightarrow \widehat{BIC}=180^{0}-\widehat{ACx}$
$\rightarrow \widehat{BIC}=180^{0}-60^{0}=120^{0}$
