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# Core 2 Trigonometry question watch

1. Hi guys, I am having trouble with solving trig equations. I get the value of a but i always struggle in getting a final result. On the markscheme for example it says 360-a for some but 360+a for others. Is there a rule i need to remember for each trigonometric function?
2. (Original post by ijoell)
Hi guys, I am having trouble with solving trig equations. I get the value of a but i always struggle in getting a final result. On the markscheme for example it says 360-a for some but 360+a for others. Is there a rule i need to remember for each trigonometric function?
See page 3 in the attachment. Does it help? Please let me know.
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3. Trigonometry.pdf (744.4 KB, 85 views)
4. (Original post by ijoell)
Hi guys, I am having trouble with solving trig equations. I get the value of a but i always struggle in getting a final result. On the markscheme for example it says 360-a for some but 360+a for others. Is there a rule i need to remember for each trigonometric function?
It honestly depends on what trig function you are using. Tip: Always draw a graph in trigonometry questions.

The reason behind it being either 360-a or 360+a is due to the graphs. For example if you draw a sine graph and draw a straight line from where sin^-1(x)=a and look at where the straight line intersects with the sine curve. The first intersection will be sin^-1(x), then see if the intersection is behind or in front of 360/180/etc. Because it is sine it is 180-a.

cosine is 360-a.

Tan changes with each point. So just draw a graph.

The logic behind this is that imagine you are finding the angles of which you got for sin^-1(x), in the exam they usually give a range of 0<x<360 so you don't go on infinitely. You have to find the points where the line intersects the points before the range. So the answer is very unlikely just too be one angel but rather 2.

Hope this helps!
5. tan solutions will tend to happen for, say, the given solution "t", plus and minus every 180 degrees:

sin solutions (assuming you have taken account of what your calculator says - e.g.
degrees by calculator - but is actually 180 + 60 = 240 degrees by CAST diagram.

you roughly sketch the sin graph, and see on it that there is a corresponding angle at what MUST be 360 - 60 degrees.

If you do this (taking into account the CAST diagram), you can`t go wrong.

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