Giải Bài 1 trang 22

Đề bài

Tính:

a) ${\left(3x+4\right)}^2$                                 

b) ${\left(5x-y\right)}^2$                                  

c) ${\left(xy-\frac{1}{2}y\right)}^2$

Lời giải chi tiết

a) ${\left(3x+4\right)}^2={\left(3x\right)}^2+2.3x.4+4^2=9x^2+24x+16$

b) ${\left(5x-y\right)}^2={\left(5x\right)}^2-2.5x.y+y^2=25x^2-10xy+y^2$

c) ${\left(xy-\frac{1}{2}y\right)}^2={\left(xy\right)}^2-2.xy.\frac{1}{2}y+{\left(\frac{1}{2}y\right)}^2=x^2{y}^2-x{y}^2+\frac{1}{4}{y}^2$