a. \(36-12x+x^2=6^2-2.6.x+x^2=\left(6-x\right)^2\)
b. \(4x^2+12x+9=\left(2x\right)^2+2.2x.3+3^2=\left(2x+3\right)^2\)
c: \(=-\left(25x^6-10x^3y^4+y^8\right)\)
\(=-\left(5x^3-y^4\right)^2\)
d: \(=\left(\dfrac{1}{2}x\right)^2-2\cdot\dfrac{1}{2}x\cdot5y+\left(5y\right)^2=\left(\dfrac{1}{2}x-5y\right)^2\)