косинус во второй четверти отрицательный,
sin^2B=0,64
cos^2B=1-sin^2b=1-0,64=0,36
cosB=-0,6
sin(П/4+B)=sinП/4cosB+cosП/4sinB=
=√2/2(0,8-0,6)=(√2/2)*0,2=√2*0,1≈0,144
15х+15=0
15х=-15
х=-15:15
х=-1
D = 12*12+9*4*5 = 324
x1 = (12+18)/9*2 = 5/3 = 1 2/3
x2 = (12-18)/9*2 = -6/18 = -1/3
4,8d^3+6,4d^2-2,4d
d(4,8d^2+6,4d)
Х^4 + x³ + 6x² + 5x + 5 = x^4 + x³ + 5x² + x² + 5x + 5 = x²(x² + x + 1) + 5(x² + x + 1)=(x²+x+1)(x²+5)