2,8-3,1-4,9-4,2=-0,3-9,1=-9,4. 0,3*2\7+0,3*5\7=0,3. 2х-2=0, 2х=2, х=1. 6х-7=15+2х, 6х-2х=15+7, 4х=22, х=5,5.
(7+d)(d-7)+(d+3)(3-d)+40(d+1)=7d-49+d²-7d+3d-d²+9-3d+40d+40=-49+d²-d²+9+40d+40=-49+9+40×0,5+40=40×0,5=20.
sin5x-sin3x=0
2sinxcos4x=0
1) sinx=0 , x =<span>πn, </span>
<span>2) cos4x=0, 4x=<span>π/2 +<span>πn, x=<span>π/8+<span>π/4n</span></span></span></span></span>