1)3x³+8x²-15x-40=0
x²(3x+8)-5(3x+8)=0
(3x+8)(x²-5)=0
a)3x+8=0,x=-8/3
b)x²-5=0, (x+√5)(x-√5)=0, x= -√5,x=+√5
Otvet: x1=-8/3, x2=-√5,x3=√5
2)(x²+2x)²-10(x²+2x)+21=0
(x²+2x)=z
z²-10z+21=0,D=100-84=16, √D=√16=4
z1=(10+4)/2=14/2=7,z1=7
z2=(10-4)/2=6/2=3, z2=3
a)x²+2x=7,x²+2x-7=0,D=4+28=32=16.2,√(16.2)=4.√2
x1=(-2+4√2)/2=-1+2√2
x2=(-2-4√2)/2=-1-2√2
b)x²+2x=3,x²+2x-3=0, D=4+12=16,√16=4
x3=(-2+4)/2=2/2=1
x4=(-2-4)/2=-6/2=-3
Otvet: x1=1+2√2,x2=1-2√2, x3=1, x4=-3