A) 4*(c+5)=c+2
4c+5=c^2+4c+
c^2-1=0
c=+1 и c=-1
Б)d^2-2d+1=d+5
d^2-3d-4=0
D=9+16=25
d1=(3+5)/2=4
d2=(3-5)/2=-1
Г) 3u+1-4-u+1=0
2u-2=0
2u=2
u=1
<span>sinx/2*sin3x/2=1/2
1/2[cos(x/2 - 3x/2) - cos(x/2 + 3x/2)] = 1/2
cos(x) - cos(2x) = 1
применяем формулу: (cos2x = 2</span>cos²x - 1)<span>
2cos</span>²x - cosx = 0
cosx(2cosx - 1) = 0
1) cosx = 0
x₁ = π/2 + πk, k∈Z
2) 2cosx - 1 = 0
cosx = 1/2
x = (+ -)arccos(1/2) + 2πn, n∈Z
x₂ = (+ -)(π/3) + 2πn, n∈Z
<span>
</span>
0,7х-2,1=0,5х+0,5
0,7х-0,5х=0,5+2,1
0,2х=2,6
Х=13