10м=1000см
2 м 80 см=280см
1)1000:280=3- кусков по 280 см
2)1000-(280•3)=160- см останется
(50+7)-20=(50-20)+7=30+7=37
(70+5)-50=(70-50)+5=20+5=25
(80+9)-30=(80-30)+9=50+9=59
(40+5)-10=(40-10)+5=30+5=35
(90+8)-70=(90-70)+8=20+8=28
(50+3)-40=(50-40)+3=10+3=13
Sinx-cosx - 4cos^3sinx = 4sin^3x ->
sinx - cosx = 4sinx(cos^2x+sin^2x) = 4sinx ->
3sinx = - cosx -> sinx = - cosx/3
sinx^2 + cos^2x = 1 -> cos^2x + cos^2x/9 = 1 ->
10cos^2x = 9 -> cosx = - 3√10/10 cosx = 3√10/10
два равенства:
1. cosx = - 3√10/10 sinx = √10/10 ->
x = 3π/2+arcsin (√10/10) + 2πn
2. cosx = 3√10/10 sinx = - √10/10
x = 2π - arcsin (√10/10) + 2πn