Ответ:\((2-\sqrt{a})(2+\sqrt{a})-4=4-a-4=-a\).\((3-\sqrt{2a})(3+\sqrt{2a})+4a=9-2a+4a=9+2a\).\((2\sqrt{3}-3\sqrt{a})(2\sqrt{3}+3\sqrt{a})=12-9a\).\((2\sqrt{7}-\sqrt{7a})(2\sqrt{7}+\sqrt{7a})=28-7a\).