Đặt \(\sqrt{x^2-7x+19}-\sqrt{x^2-7x+15}=B\) = B
Xét tích \(AB=\left(\sqrt{x^2-7x+19}-\sqrt{x^2-7x+15}\right)\left(\sqrt{x^2-7x+19}+\sqrt{x^2-7x+15}\right)\)
\(=x^2-7x+19-\left(x^2-7x+15\right)=x^2-7x+19-x^2+7x-15\)
\(=4\)
Mà \(B=2\Leftrightarrow A=2\)