This is my first post and I'm really sort of stumped trying to do my homework here - it's to be in for tomorrow and I was out when it was being explained...
The sum is:
If tanA = -1, find the two values for angle A, where 0degrees <= A <= 360degrees
If anyone could explain how to do it, at Junior Cert level (Ireland), I'd really appreciate it!
I don't know how to get certain symbols (Doh)
Thanks in advance!
. This is a basic identity you should know.
Tangent is negative in the 2nd and 4th quadrant, so and . Thus .
Thank you both for your replies, but in all honesty - I didn't understand a word you said..
I checked at the back of my book and the answers are 135degrees and 315degrees
I appreciate your answers but I think they're more leaving cert level (Thinking)
Any chance you can dumb them down to Honours level 15 year old maths (Rofl)
Why wouldn't we try ? :)
Originally Posted by JT133
You HAVE to be familiar with specific values of sin and cos (and with tan, but you know that tan=sin/cos).
Here is a table you should know, it will really helps (Wink)
Well I can see that the answer is diagonally opposite on the table and I'm assuming that for example in the 135deg. that -rt2/2 is the sin value and rt2/2 is the cosine value for tan because Tan A = Sin A / Cos A and Sin A = - Cos A
I don't see how your getting that from the -1 though because Tan-1(-1) = -45
I've never been thought how to use tables for algebra just the trustworthy calculator way (Nod)
Also, as a general rule:
-45 degrees is the same thing as 315 degrees. If you go clockwise 45 degrees, it is the same thing as going counter-clockwise 315 degrees. However, -45 isnt between 0 and 360. Read up on period of trig functions on wikipedia or something.
Originally Posted by JT133
Okay well I think I'm getting it..
360 - 45 = 315 hence one of the answers
But 135... :confused:
Well this is my 1st year learning about trigonometry, I'd say from judging by your replies I only know the basics. I know that Sine = Opp/Hyp, Cosine = Adj/Hyp and Tangent = Opp/Adj
I haven't learned any formula on trigonometry except the Sine Rule and I've never had to use/or been thought about radians but I checked Wikipedia a minute ago
This is the level expected from me: http://examinations.ie/archive/examp...C003ALP2EV.pdf
Tan(A) = -1
A = Tan^-1(-1) = -45 degrees
-45 isnt within your range of answers (0<A<360), but from this graph:
you can see that when the x value = -45, there are multiple x values that give the same y value, occurring every 180 degrees (the period of the tan graph).
To find the next value, add 180 to -45 (= 135, within the range).
To find the next value, add 180 to 135 (= 315, also within the range, although not on the diagram).
Hope this helps.
Ahhh! I get it! Thanks archer90, Moo and xifentoozlerix
Thats an extra 10 marks in my state exam, which is in 2 weeks!
Tan is negative in the 2nd Quadrant; thus