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Alexlolshockp1aywd
a fost răspuns

subpunctul E.................

Subpunctul E class=

Răspuns :

Darrin2

cos(2π/9)+cos(4π/9)+cos(8π/9)=0

π/9=20°

cos40°+cos80°+cos160°=0

cos(90°-50°)+cos(90°-10°)+cos(180°-20°)=0

sin50°+sin10°-cos20°=0

2*sin(50°+10°)/2*cos(50°-10°)/2-cos20°=0

2*sin30°*cos20°-cos20°=0

cos20°(2*1/2-1)=0

cos20°(1-1)=0

0=0

Bafta!!

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