4)
(2x-y)²+(x+2y)²=
((2x)²+2•2x(-y)+(-y)²)+(x²+2x•2y+(2y)²)=
(2²•x²-2•2xy+y²)+(x²+2•2xy+2²•y²)=
(4x²-4xy+y²)+(x²+4xy+4y²)=
4x²-4xy+y²+x²+4xy+4y=
4x²+x²-4xy+4xy+y²+4y²=
5x²+5y²
[tex]5) \\ \\ 20xy ^{2}z + 16 {x}^{2}yz - 24 {xyz}^{2} = 4xyz( \frac{20 {xy}^{2}z }{4xyz} + \frac{ {16x}^{2}yz }{4xyz} + \frac{ - 24 {xyz}^{2} }{4xyz} = 4xyz(5y + 4x - 6z) [/tex]
[tex]4(x + y) + 5(x + y) - 10(x + y) = - (x + y) = - x - y[/tex]
