Thread: Law of cosines

okay i dont know why, this may be extremely easy but i'm just not getting the right answer

Here's the question:
richmond is 200 kilometers due east of Teratown and Hamilton is 150 kilometers directly north of Teratown. Find the shortest distance in kilometers between Hamilton and Richmond.

I use law of cosines right? and so what would the equation look like?

Originally Posted by kri999

okay i dont know why, this may be extremely easy but i'm just not getting the right answer

Here's the question:
richmond is 200 kilometers due east of Teratown and Hamilton is 150 kilometers directly north of Teratown. Find the shortest distance in kilometers between Hamilton and Richmond.

I use law of cosines right? and so what would the equation look like?

Pythagoras' Theorem:

.

but i have to use the law of cosines...how do i do that with this problem? or is just not possible?

Originally Posted by kri999

but i have to use the law of cosines... Mr F asks: Why?

how do i do that with this problem? or is just not possible?

OK:



In case you haven't guessed, Pythagoras' Theorem is a special case of the cosine rule.

Thank you! I got the same equation but somehow I keep getting the answer wrong, but i just tried a differnet method and it worked out..
yeah i have to use law of cosines because that's what the chapter's on haha

thanks so much!

Originally Posted by mr fantastic

OK:



In case you haven't guessed, Pythagoras' Theorem is a special case of the cosine rule.

I actually didn't know that. I just kinda figured he sat around playing with blocks and rulers for a few weeks until a lightbulb turned on.