Răspuns:
Explicație pas cu pas:
a) sin×30°+sin45°×cos45°-cos60°=1/2+√2/2x√2/2-1/2=2/4=1/2
b)cos10°+cos 20° +cos160°+cos170°=(cos10°+cos170°)+(cos20°+cos160°)
=2cos(10°+170°)/2cos(170°-10°)/2+2cos(160°+20°)/2cos(160°-20°)/2=
=2 cos90°cos80° +2 cos90° cos70° = 0 cos 90°=0
c)sin ² 130grade+cos ² 50 grade
sin 130°=sin (180°-50°)=sin 50°
sin ² 130grade+cos ² 50 grade=sin ²50°+cos²50°=1
d)cosx=4/5 sin x=√1-cos²x=√1-16/25=√9/25 sin x=3/5
