sin^2 x=1-cos^2 x
6*(1-cos^2 x) - 5cosx + 5=0
6-6cos^2 x - 5cos x + 5=0
-6cos^2x-5cos x + 11=0
6cos^2 x + 5 cos x -11=0
cos x=y
6y^2+5y-11=0
D= 289
y1=(-5+17)/12=1
y2= (-5-17)/12=-11/6 - не подходит, т.к. -1<=сos x<=1
cos x=1
x=0
2x^2 - 20x + 18 = 0 // : 2
x^2 - 10x + 9 = 0
D = 100 - 36 = 64 = 8^2
x1 = ( 10 + 8)/2 = 18/2 = 9;
x2 = ( 10 - 8)/2 = 2/2 = 1;
((3х-2)/(5x+8))`=(3(5x+8)-5(3x-2))/(5x+8)²=34/(5x+8)²
1) x³+6x²+12x+8-(x³-6x²+12x-8)=12x²+4x
x³+6x²+12x+8-x³+6x²-12x+8=12x²+4x
12x²+16=12x²+4x
16=4x
4x=16
x=4
2) x³+9x²+27x+27-(x³-12x²+48x-64)=21x²+7
x³+9x²+27x+27-x³+12x²-48x+64=21x²+7
21x²-21x+91=21x²+7
-21x+91=7
-21x=7-91
-21x=-94
x=4