<span>сos(x-y)=1 </span>
<span>вычитаете </span>
<span>cos(x+y)=-1/2 </span>
<span>x-y=2пк </span>
<span>x+y=2п/3+ 2пm </span>
<span>x-y=2пк </span>
<span>x+y=-2п/3+2пm</span>
D=42-7/15-1=35/14=2,5
b12=b1+d11=7+2,5*11=34,5
b13=7+2,5*12=37
b14=7+2,5*13=39,5
b15=42
b16=44,5
b17=47
b18=49,5
b19=52
b20=54,5
400,5