\(\left(4x^2-7x-50\right)^2-16x^4-56x^3-49x^2\)
\(=\left(4x^2-7x-50\right)^2-\left(4x^2\right)^2-2.4x^2.7x-\left(7x\right)^2\)
\(=\left(4x^2-7x-50\right)^2-\left(4x^2-7x\right)^2\)
\(=\left(4x^2-7x-50-4x^2+7x\right)\left(4x^2-7x-50+4x^2-7x\right)\)
\(=-50\left(8x^2-14x-50\right)\)