Question

điền vào chỗ trống ( giải thích hẳn ra vì sao )

a) (2x -5y)^2 = 4x^2 - 20xy + .....

b) (....+....)(x - 3y) = x^2 - 9y^2

c) (x-y)^2 = (....-x)^2

Answer 1

a) (2x - 5y)² = 4x² - 20x + 25y²

b) (x + 3y)(x - 3y) = x² - 9y²

c) (x - y)² = (y - x)²

Answer 2

a) ( 2x -5y )² = 4x² -20xy + 25y²

b) (x + 3y ).(x - 3y ) =x² - 9y²

c) (x - y )² = (y -x)²

Answer 3

\(a,\left(2x-5y\right)^2=\left(2x\right)^2-2.2x.5y+\left(5y\right)^2\)

\(=4x^2-20xy+25y^2\)

\(b,\left(...+...\right)\left(x-3y\right)=x^2-\left(3y\right)^2\)

\(=\left(x+3y\right)\left(x-3y\right)=x^2-9y^2\)

\(c,\left(x-y\right)^2=\left(...-x\right)^2\)

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

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