\(a,=8xy\left(2x+1\right)\\ b,=x\left(x-7\right)+y\left(x-7\right)=\left(x+y\right)\left(x-7\right)\\ c,=49-\left(x-4\right)^2=\left(7-x+4\right)\left(7+x-4\right)\)
a) \(=8xy\left(2x+1\right)\)
b) \(=x\left(x-7\right)+y\left(x-7\right)=\left(x-7\right)\left(x+y\right)\)
c) \(=49-\left(x^2-8x+16\right)=49-\left(x-4\right)^2\)
\(=\left(7-x+4\right)\left(7+x-4\right)=\left(11-x\right)\left(x+3\right)\)
\(8xy\left(2x+1\right)\)
\(x\left(x-7\right)+y\left(x-7\right)=\left(x+y\right)\left(x-7\right)\)