\(\text{a},=25x^2-9+5x^2-5x=30x^2-5x-9\\ b,=x^2+8x+16-x^2+1-16=8x+1\\ c,=4x^2-4x+1+x^2+6x+9-5\left(x^2-49\right)=5x^2+2x+10-5x^2+245=2x+255\)
a: \(=25x^2-9+5x^2-5x=30x^2-5x-9\)
b: \(=x^2+8x+16-x^2+1-16=8x+1\)
c: \(=4x^2-4x+1+x^2+6x+9-5x^2+245=2x+255\)