36-12х+х^2-х^2-12х=0
36-24х=0
36-24*1/24=35
Если pi < A < 3pi/2, то А находится в 3 четверти, sin A < 0, cos A < 0
sin A = -1/√65
cos A = -√(1 - sin^2 A) = -√(1 - 1/65) = -√(64/65) = -8/√65
ctg A = cos A / sin A = (-8/√65) / (-1/√65) = 8/√65 * √65/1 = 8
5*ctg A = 5*8 = 40
X^2 + 2x - 15 = 0
D = 4 + 60 = 64
x1 = ( - 2 + 8)/2 = 6/2 = 3
x2 = ( - 2 - 8)/2 = - 10/2 = - 5
x^2 + 2x - 15 = (x + 5)(x - 3)