Simplify the following expressions :
$(i)$ $(5+\sqrt{7})(2+\sqrt{5})$
$(ii)$ $(5+\sqrt{5})(5-\sqrt{5})$
$(iii)$ $(\sqrt{3}+\sqrt{7})^{2}$
$(iv)$ $(\sqrt{11}-\sqrt{7})(\sqrt{11}+\sqrt{7})$

$(i)$ Using the distributive property: $(5+\sqrt{7})(2+\sqrt{5}) = 5(2) + 5(\sqrt{5}) + \sqrt{7}(2) + \sqrt{7}(\sqrt{5}) = 10 + 5\sqrt{5} + 2\sqrt{7} + \sqrt{35}$.
$(ii)$ Using the identity $(a+b)(a-b) = a^2 - b^2$: $(5+\sqrt{5})(5-\sqrt{5}) = 5^2 - (\sqrt{5})^2 = 25 - 5 = 20$.
$(iii)$ Using the identity $(a+b)^2 = a^2 + 2ab + b^2$: $(\sqrt{3}+\sqrt{7})^2 = (\sqrt{3})^2 + 2(\sqrt{3})(\sqrt{7}) + (\sqrt{7})^2 = 3 + 2\sqrt{21} + 7 = 10 + 2\sqrt{21}$.
$(iv)$ Using the identity $(a-b)(a+b) = a^2 - b^2$: $(\sqrt{11}-\sqrt{7})(\sqrt{11}+\sqrt{7}) = (\sqrt{11})^2 - (\sqrt{7})^2 = 11 - 7 = 4$.