Question

Answer 1

\(M=\left(x-2y\right)^2=\left(18-2.4\right)^2=10^2=100\)

\(N=\left(2x-y\right)^3=\left(2.6-\left(-8\right)\right)^3=20^3=8000\)

\(\left(x+2\right)\left(x-2\right)-\left(x-3\right)\left(x+1\right)=x^2-4-\left(x^2-2x-3\right)=x^2-4-x^2+2x+3=2x-1\)

\(\left(2x+1\right)^2+\left(3x-1\right)^2+2\left(2x+1\right)\left(3x-1\right)=\left(2x+1+3x-1\right)^2=\left(5x\right)^2=25x^2\)

Answer 2

Bài 77:

a: Ta có: \(M=x^2-4xy+4y^2\)

\(=x^2-2\cdot x\cdot2y+\left(2y\right)^2\)

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

\(=\left(18-2\cdot4\right)^2\)

\(=10^2=100\)

b: Ta có: \(N=8x^3-12x^2y+6xy^2-y^3\)

\(=\left(2x\right)^3-3\cdot\left(2x\right)^2\cdot y+3\cdot2x\cdot y^2-y^3\)

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

\(=\left(2\cdot6+8\right)^3\)

\(=20^3=8000\)