Cos105° +cos105°=2cos105° ~ -0.48
{7x+y=20
{x-5y=8
{7(5y+8)+y=20
{x=5y+8
{35y+56+y=20
{x=5y+8
{36y=-36
{x=5y+8
{y=-1
{x=5(-1)+8
{y=-1
{x=3
<u>Ответ: (3;-1)</u>
{3x+7y=-5|*5
{5x+4y=7|*(-3)
{15x+35y=-25
{<u>-15x-12y=-21 </u>+
23y=-46
y=-46:23
y=-2
5x+4*(-2)=7
5x-8=7
5x=8+7
5x=15
x=3
Ответ: (3;-2)
{2-4y=3(x-2)
{2(x+y)=5y+2,5
{2-4y=3x-6
{2x+2y=5y+2,5
{3x+4y=8|*2
{2x-3y=2,5|*(-3)
{6x+8y=16
{<u>-6x+9y=-7,5 </u>+
17y=8,5
y=8,5/17
y=0,5
3x+4*0,5=8
3x+2=8
3x=8-2
3x=6
x=6:3
x=2
Ответ: (2;0,5)
y'=x'cosx+x(c0sx)'+ (3x)'=cosx-xsinx+3
Решение
3cos2x = 2cosx
3*(2cos²x - 1) - 2cosx = 0
6cos²x - 2cosx - 3 = 0
cosx = t
6t² - 2t - 3 = 0
D = 4 + 4*6*3 = 76
t₁ = (2 - 2√19)/12
t₁ = (1 - √19)/6
t₂ = (1 +√19)/6
1) cosx = (1 - √19)/6
x₁ =(1 - √19)/6 + 2πk, k∈Z
2) cosx = (1 + √19)/6
x₂ = (1 + √19)/6 + 2πn, n∈Z