a: \(9x^2+30x+25=\left(3x+5\right)^2\)
b: \(\dfrac{4}{9}x^4-16x^2=x^2\left(\dfrac{4}{9}x^2-16\right)=x^2\left(\dfrac{2}{3}x-4\right)\left(\dfrac{2}{3}x+4\right)\)
c: \(\dfrac{12}{5}x^2y^2-9x^4-\dfrac{4}{25}y^4\)
\(=-\left(9x^4-\dfrac{12}{5}x^2y^2+\dfrac{4}{25}y^4\right)\)
\(=-\left(3x^2-\dfrac{2}{5}y^2\right)^2\)