a, \(\left(x-15\right)\left(x+15\right)-\left(x+2\right)^2-\left(x-5\right)^2\)
\(=x^2-225-x^2-4x-4-x^2+10x-25\)
\(=-x^2+6x-254\)
b, \(\left(2x-1\right)\left(2x+1\right)+\left(x+9\right)^2-\left(x-3\right)^2\)
\(=4x^2-1+x^2+18x+81-x^2+6x-9=4x^2+24x+71\)
c, \(\left(7x-3\right)^2-\left(x-5\right)\left(x+5\right)-\left(2x+4\right)^2\)
\(=49x^2-42x+9-x^2+25-4x^2-16x-16=44x^2-58x+18\)