Hello there i am writing cause i was handed this special task by my teacher, and i do not quite know how to handle it..

I was basically handed a picture of a triangle, with a square inside. As shown on the picture below!

As you see the square is a 1 by 1 and the length of |BA|is 10

So here comes the question, how do i find the length of |BC| in this triangle ?

Thanks for trying to help me!