## Thinking Mathematically (6th Edition)

$\sqrt 7$
We start with $\sqrt 63$ - $\sqrt 28$ We can write 63 as 9 x 7 ( a perfect square times a number) We can write 28 as 4 x 7 (a perfect square times a number) Rewriting the problem, we have: $\sqrt{ 9\cdot 7}$ - $\sqrt {4 \cdot 7}$ We can take the square root of 9 and of 4; this gives us 3 and 2. Once we take the square root of a number under a radical sign, the square root is written on the outside of the radical, like this: 3$\sqrt 7$ - 2$\sqrt 7$ We can now subtract (since the radical parts are exactly alike). We get $\sqrt 7$