b)\(\left(x-5y\right)^2-\left(x+3y\right)^2=\left(x-5y-x-3y\right)\left(x-5y+x+3y\right)\\ =-8y\left(2x-2y\right)=-16\left(x-y\right)\)
c) \(x^2-64=x^2-8^2=\left(x-8\right)\left(x+8\right)\)
d)\(y^{2-100}=y^2:y^{100}=\dfrac{y^2.1}{y^{100}}=\dfrac{1}{y^{98}}\)
e)\(y^2-100=y^2-10^2=\left(y-10\right)\left(y+10\right)\)