b) ... = \(\left(7x-4-2x+1\right)\left(7x-4+2x-1\right)\) = \(\left(5x-3\right)\left(9x-5\right)\)
d) ... = \(\left(x^2+6x+9\right)-\left(y^2-2y+1\right)=\left(x+3\right)^2-\left(y-1\right)^2=\left(x+3-y+1\right)\left(x+3+y-1\right)\)
\(=\left(x-y+4\right)\left(x+y+2\right)\)
