a,^ACB=^MHE=900 =>dpcmta co DO va BE cung vuong goc voi AE =>DO//BE
b, ta co CB=CD (gt)
^DCK=^BCE(dd);^CDK=^CBE(sole) =>dpcm
c,ta co^DHE=900;^CEA=450(nhin cung 1/4 duong tron)=>dpcm
=>C la tam duong tron ngooai tiep KHE=>^CMN=^CHE=^CEH=^CBA=^CAB
=>dpcm