a/ \(=\left(\frac{a}{2}\right)^2+2.\frac{a}{2}.10b+\left(10b\right)^2=\left(\frac{a}{2}+10b\right)^2\)
b/ \(=\left(x+y\right)^3+z^3-3xy\left(x+y\right)-3xyz\)
\(=\left(x+y+z\right)\left(\left(x+y\right)^2-z\left(x+y\right)+z^2\right)-3xy\left(x+y+z\right)\)
\(=\left(x+y+z\right)\left(x^2+y^2+z^2-xy-yz-zx\right)\)