I have a question, can anyone solve this equation step by step and explain?

Code:
I/{sqrt[(x-10)^2+(y-0)^2]}^2=2I/{sqrt[(x-20)^2+(y-0)^2]}^2
If you want you can turn to page 578 on Algebra 2 book, it mentioned there, I do not understand how after simplify, it can form x^2+y^2=200

Thanks