Sin12x+sin13x=0
2sin((12x+13x)/2)*cos((13x-12x)/2)=0
sin25x/2=0 cosx/2=0
25x/2=pik x/2=pi/2+pik
x=2pik/25 x=pi+2pk
180*2/25=14.4°
2x^2+3x = 2x^2+21
3x = 21
x = 7
(3x+1)(4x-5) = 12x^2-13x+1
12x^2-11x-5 = 12x^2-13x+1
2x = 6
x = 3
(2x-3)(3x+7)-(x-5) = 12x^2-13x+1
6x^2+14x-9x-21-x+5 = 12x^2-13x+1
-6x^2+17x = 17
x(17-6x) = 17
0,37х+74-0,97х=158
74-0,97х+0,37х=158
74-0,6х=158
-0.6х=158-74
-0.6х=84
х=-140