Question

CMR

a)(3x-5)(3x+5)=9x^2-25

b)x^3-y^3=(x-y)(x^2+xy+y^2)

c)x^2+y^2=(x+y)^2-2xy

Answer 1

a) \(\left(3x-5\right)\left(3x+5\right)=9x^2-25\Leftrightarrow9x^2+15x-15x-25=9x^2-25\Leftrightarrow9x^2-25=9x^2-25\)(đúng)

b) \(x^3-y^3=\left(x-y\right)\left(x^2+xy+y^2\right)\Leftrightarrow x^3-y^3=x^3+x^2y+xy^2-x^2y-xy^2-y^3\Leftrightarrow x^3-y^3=x^3-y^3\)(đúng)

c) \(x^2+y^2=\left(x+y\right)^2-2xy\Leftrightarrow x^2+y^2=x^2+y^2+2xy-2xy\Leftrightarrow x^2+y^2=x^2+y^2\)(đúng)

Answer 2

a: \(\left(3x-5\right)\left(3x+5\right)\)

\(=9x^2+15x-15x-25\)

\(=9x^2-25\)

b: \(\left(x-y\right)\left(x^2+xy+y^2\right)\)

\(=x^3+x^2y+xy^2-x^2y-xy^2-y^3\)

\(=x^3-y^3\)

c: \(\left(x+y\right)^2-2xy\)

\(=x^2+2xy+y^2-2xy\)

\(=x^2+y^2\)