a,$\widehat{ACB}=\widehat{MHE}=90^0$ =>dpcmta co DO va BE cung vuong goc voi AE =>DO//BE
b, ta co CB=CD (gt)
$\widehat{DCK}=\widehat{BCE}(dd);\widehat{CDK}=\widehat{CBE}(so le)$ =>dpcm
c,ta co$\widehat{DHE}=90^0;\widehat{CEA}=45^0$(nhin cung 1/4 duong tron)=>dpcm
=>C la tam duong tron ngooai tiep KHE=>$\widehat{CMN}=\widehat{CHE}=\widehat{CEH}=\widehat{CBA}=\widehat{CAB}$
=>dpcm