Question

please answer asap
thank you

Answer 1

I don't know if this is how i'm supposed to explain it, but AC is twice the size of DF, and DF is twice the size of CF

Pretend that DF is 2 inches, then AC is 4 inches and CF is 1 inch, so you get this:
${DC}^{2} = CF \times AC$
${2}^{2} = 1 \times 4$