试说明角A+角B=角C+角D+角E+角F

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试说明角A+角B=角C+角D+角E+角F

试说明角A+角B=角C+角D+角E+角F
试说明角A+角B=角C+角D+角E+角F
 

试说明角A+角B=角C+角D+角E+角F
连结CD, 有
A + B = 180 - AMB = 180 - CMD = MCD + MDC = (MCN + NCD) + (MDN + NDC) = (NCD + NDC) + (MCN + MDN) = (180 - CND) + (MCN + MDN) = (180 - ENF) + (MCN + MDN) = (E + F) + (C + D)