Factor $490=7^{2}\times 10$. Rewrite the square root of the product $\sqrt{7^{2}\times 10}$ as the product of square roots $\sqrt{7^{2}}\sqrt{10}$. Take the square root of $7^{2}$.
$$7\sqrt{10}+\sqrt{90}-\sqrt{250}$$
Factor $90=3^{2}\times 10$. Rewrite the square root of the product $\sqrt{3^{2}\times 10}$ as the product of square roots $\sqrt{3^{2}}\sqrt{10}$. Take the square root of $3^{2}$.
$$7\sqrt{10}+3\sqrt{10}-\sqrt{250}$$
Combine $7\sqrt{10}$ and $3\sqrt{10}$ to get $10\sqrt{10}$.
$$10\sqrt{10}-\sqrt{250}$$
Factor $250=5^{2}\times 10$. Rewrite the square root of the product $\sqrt{5^{2}\times 10}$ as the product of square roots $\sqrt{5^{2}}\sqrt{10}$. Take the square root of $5^{2}$.
$$10\sqrt{10}-5\sqrt{10}$$
Combine $10\sqrt{10}$ and $-5\sqrt{10}$ to get $5\sqrt{10}$.
