Question

cần gấp ạ

Answer 1

Bài 5:

a: \(\left(x-1\right)^3-x\left(x-3\right)^2-3x^2=5\)

=>\(x^3-3x^2+3x-1-x\left(x^2-6x+9\right)-3x^2=5\)

=>\(x^3-6x^2+3x-1-x^3+6x^2-9x=5\)

=>-6x-1=5

=>-6x=6

=>x=-1

b: \(\left(x+2\right)^3-x^2\left(x+6\right)=-4\)

=>\(x^3+6x^2+12x+8-x^3-6x^2=-4\)

=>12x+8=-4

=>12x=-12

=>x=-1

Bài 4:

a: \(\left(x+1\right)^3-x^2\left(x+3\right)\)

\(=x^3+3x^2+3x+1-x^3-3x^2\)

=3x+1

b: \(\left(x-2\right)^3-x\left(x+1\right)\left(x-1\right)+6x^2\)

\(=x^3-6x^2+12x-8-x\left(x^2-x\right)+6x^2\)

\(=x^3+12x-8-x^3+x^2=x^2+12x-8\)

Bài 3:

a: \(A=x^3+12x^2+48x+64\)

\(=x^3+3\cdot x^2\cdot4+3\cdot x\cdot4^2+4^3\)

\(=\left(x+4\right)^3\)

Khi x=6 thì \(A=\left(6+4\right)^3=10^3=1000\)

b: \(B=x^3-6x^2+12x-8\)

\(=x^3-3\cdot x^2\cdot2+3\cdot x\cdot2^2-2^3\)

\(=\left(x-2\right)^3\)

Thay x=22 vào B, ta được:

\(B=\left(22-2\right)^3=20^3=8000\)

c: \(C=x^3+3x^2+3x\)

\(=x^3+3x^2+3x+1-1\)

\(=\left(x+1\right)^3-1\)

Thay x=29 vào C, ta được:

\(C=\left(29+1\right)^3-1=30^3-1=27000-1=26999\)

d: \(D=x^3-9x^2+27x-26\)

\(=x^3-9x^2+27x-27+1\)

\(=\left(x-3\right)^3+1\)

Thay x=23 vào D, ta được:

\(D=\left(23-3\right)^3+1=20^3+1=8000+1=8001\)