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2014-06-15T17:21:45+03:00
M(A)=m(B)=x°
m(C)+m(D)=180°
51°+ m(D)=180°
m(D)=129°
m(A)+m(B)+m(C)+m(D)=360°
2x°+51°+129°=360°
2x°=180
x°=90°
rezulta m(A)=90°
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