Răspuns :

Andreutsa10id

cos210= cos(180+30)=

cos 180×cos30 -sin 180× sin 30=

-1×rad3/2 -0×1/2=-rad3/2

sin 135= sin(90+45)=

sin90×cos45 + cos 90×sin 45=

1×rad2/2+0×rad2/2=rad2/2

cos75= cos(30+45)=

cos30×cos45-sin30×sin45

rad3/2×rad2/2 - 1/2×rad2/2= rad6/4-rad2/4= (rad6-rad2)/4

Targoviste44id

[tex]\it cos75^o=sin15^o=\dfrac{\sqrt6-\sqrt2}{4}\\ \\ \\ sin135^o=sin(180^o-135^o)=sin45^o=\dfrac{\sqrt2}{2}\\ \\ \\ cos210^o=cos(180^o+30^o)=cos180^ocos30^o-sin180^osin30^o=\\ \\ \\ =-1\cdot\dfrac{\sqrt3}{2}-0=-\dfrac{\sqrt3}{2}[/tex]

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