Se dă triunghiul isoscel ABC (AB=AC) in care m(∢A)=20°, D ∊(AB) astfel încât AD = BC. Fie M ∊(AB) cu m(∢BCM)=20° şi N ∊(AC) cu m(∢NMC)=60°.
Să se determine m(∢CDN).
Research done by Rob Gratton, UCL Academy coordinator
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