Question

tính 

a) (x+2y)²

b) (x-3y)(x+3y)

c) (5-x)²

Answer 1

a)  \(\left(x+2y\right)^2=x^2+4xy+4y^2\)

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

c)  \(\left(5-x\right)=25-10x+x^2\)

Answer 2

a) \(\left(x+2y\right)^2=x^2+2.x.2y+\left(2y\right)^2=x^2+4xy+4y^2\)

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

c) \(\left(5-x\right)^2=5^2-2.x.5+x^2=25-10x+x^2\)