a. x2 - 11 = \(x^2-\left(\sqrt{11}\right)^2=\left(x-\sqrt{11}\right)\left(x+\sqrt{11}\right)\)
b. x2 - 5 = \(x^2-\left(\sqrt{5}\right)^2=\left(x-\sqrt{5}\right)\left(x+\sqrt{5}\right)\)
c. x2 - 7 = \(x^2-\left(\sqrt{7}\right)^2=\left(x+\sqrt{7}\right)\left(x-\sqrt{7}\right)\)