А) 30/100=0.30
40-30=10
10/0.30=33.33333≈33.3\%
б) 40/100=0.40
10/0.40=25\%
(4.6-x)*19=4,18
87.4-19x=4.18
-19x=4.18-87.4
-19x=-83.22
x=-83.22:(-19)
x=4.38
<em />cos²x-sin²x=0
cos²=√1-sin²
1-sin²-sin²=0
1-2sin²=0
2sin²=1
sin²x=1/2
x=+-√1/2
x=+-√2/2
x=π/4+πk
√1-x²=0
1-x²=0
x³=1
x=+-√1