-12+20z=18z-7
20+18z+-7+12
2z=5
z=5/2
z=2.5
<span>cos14п\3=cos2π/3=-cosπ/3=-1/2
</span>sin25п\6=sinπ/6=1/2
<span>tg17п\4=tgπ/4=1
4*(-1/2)-1/2+1=-2-1/2+1=-1 1/2
</span>
( 990 / X ) - ( 990 / ( X - 9 )) = - 1
990 * ( X - 9 ) - 990X = - X^2 + 9X
X^2 - 9X - 8910 = 0
D = 81 + 3560 = 35721 ; √ D = 189
X1 = ( 9 + 189 ) : 2 = 99
X2 < 0
Cкорость первого 99 ( км/час )