1) 3:х=1
Х=3:1
Х=3
2)5х+2:2х+5=-1
5х+х+5=-1
6х+5=-1
6х=-1-6
6х=-6
х=-6:6
х=-1
Я решил на листочке, прикрепленном ниже.
y'(x) = 6x^2 - 6x - 36 = 0
6(x^2 - x - 6) = 0
6(x - 3)(x + 2) = 0
x1 = -2; y(-2) = 2(-8) - 3*4 - 36(-2) + 40 = -16 - 12 + 72 + 40 = 84
x2 = 3; y(3) = 2*27 - 3*9 - 36*3 + 40 = 54 - 27 - 108 + 40 = -41
D=5
a₁=-4,8
S₁₅=n*(a₁+a₁₅)/2=15*(-4,8-4,8+5*14)/2=15*(-9,6+70)/2=(70*15-15*9,6)/2=35*15-15*4,8=15(35-4,8)=15*30,2=453