"Must Know" Trig Identities

This forum made possible through the generous support of SDN members, donors, and sponsors. Thank you.

BrazilianRider

Full Member
10+ Year Member
Joined
Oct 28, 2013
Messages
774
Reaction score
938
Just wondering which Trig Identities I MUST know before I head into my DAT next Monday? Thanks a ton guys!

Members don't see this ad.
 
All of them? Trig identities are not hard to memorize, plus you can derive them from each other (would NOT recommend doing this on the DAT, unless you found yourself with copious amounts of time and in a pinch).
 
http://en.wikipedia.org/wiki/Mnemonics_in_trigonometry

Learn the unit circle (you are guaranteed to need it on the QR), the graphic with the triangles on the Wiki page, and which quadrants are + or - and you should be fine.
That's awesome! I have never seen that before. OP, forget what I said, if you're struggling - just memorize the two grpahics and what they mean. For the quadrants, I use the mnemonic "All Students Take Calculus".
 
Members don't see this ad :)
Way past OP's test date, but on the off chance that anyone having trouble with trig identities stumbled upon this and is having trouble memorizing the graph, I actually find it easier to think of the whole thing like a regular graph - you already know what that looks like, so you can just derive everything from that knowledge.

Quadrant I: You know by looking at the graph that x-values (cos) and y-values (sin) are positive. Therefore, it also follows that tan will be positive as well.

Quadrant II: x (cos) is negative, while y (sin) is positive. Therefore tan will be negative.

Quadrant III: x (cos) and y (sin) are negative. Therefore tan will be positive.

Quadrant IV: x (cos) is positive, while sin is negative. Therefore tan will be negative.
 
  • Like
Reactions: 1 user
Jesus, I wish I woulda seen these replies earlier... I had one trig identity question and I just guessed lmao... Guess that's why I got a 19 :p
 
Top