\(100x^2-\left(x^2+25\right)^2\)
\(=\left(10x\right)^2-\left(x^2+25\right)^2\)
\(=\left(10x-x^2-25\right)\left(10x+x^2+25\right)\)
\(=\left[-\left(-10x+x^2+25\right)\right]\left(10x+x^2+25\right)\)
\(=\left[-\left(x^2-2.x.5+5^2\right)\right]\left(x^2+2.x.5+5^2\right)\)
\(=-\left(x-5\right)^2\left(x+5\right)^2\)
P/s: Ko chắc!