British Flag Theorem

Oh that sounds like a fun theorem... What is it?

It says that $AT^2+CT^2=BT^2+DT^2$, meaning that $225+625=400+DT^2$, so $DT=\sqrt{450}=\boxed{15\sqrt{2}}$.

equinox145111 wrote: Oh that sounds like a fun theorem... What is it? https://artofproblemsolving.com/wiki/index.php?title=Category:Theorems See here to learn more about theorems found in problem solving.

$AT^2+CT^2=BT^2+DT^2 \Rightarrow 15^2+25^2=20^2+DT^2$ $225+625=400+DT^2 \Rightarrow DT^2=450 \Rightarrow DT= \sqrt{450}$ $\blacksquare$