how would I write 4/√7 with a fraction whose denominator is even?
Thanks
If you think about it another way - you need to multiply top and bottom by $\displaystyle \sqrt{7}$ to rationalise the denominator. However, 7 is not an even number so you must multiply top and bottom by $\displaystyle 2$ since multiplying any integer by 2 gives an even number.
Plato did the same thing but combined the steps