### Video Transcript

What is π΄π· squared equal to?

Some of you when you look at this triangle might immediately start thinking about algebra and substitution. And if you try to do this that way, youβre going to spiral down into a very long trail of substitution. There is a more simple way to approach this.

Weβre going to set up a proportion. Hereβs triangle π΄π΅π· and triangle π΄π·πΆ. Proportionally, π΅π· over π΄π· would be equal to π΄π· over πΆπ·. Once we have this proportion β π΅π· over π΄π· is equal to π΄π· over πΆπ· β we can cross-multiply. π΄π· times π΄π· is equal to π΅π· times πΆπ·. π΄π· times π΄π· is equal to π΄π· squared, which is equal to π΅π· times πΆπ·.