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# c2 trigonometrical identities and simple equestions

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1. cos3q=-1 (q is the degree)
the answers are 60, 180 and 300
so i dont know how to solve this
this what i did, the intervals 3*0 and 3*360=1080
so my values are 180 , 360 , 540, 720, 900, 1080.
cos3q=180 , 360 , 540, 720, 900, 1080
(divide by 3)=60, 120, 180, 300, 360
2. (Original post by reb0xx)
cos3q=-1 (q is the degree)
the answers are 60, 180 and 300
so i dont know how to solve this
this what i did, the intervals 3*0 and 3*360=1080
so my values are 180 , 360 , 540, 720, 900, 1080.
cos3q=180 , 360 , 540, 720, 900, 1080
(divide by 3)=60, 120, 180, 300, 360

The interval is,
The interval for '3q' is

Solving will give us 3 solutions. One solution you will get from the calculator the other two solutions can be found by adding 360 and 720 to the calculator value. Now divide the solutions by 3 to get the required values of 'q'.

Below is the graph of y=cos(3q), this shows that it has 3 solution in the interval .

3. (Original post by reb0xx)
cos3q=-1 (q is the degree)
the answers are 60, 180 and 300
so i dont know how to solve this
this what i did, the intervals 3*0 and 3*360=1080
so my values are 180 , 360 , 540, 720, 900, 1080.
cos3q=180 , 360 , 540, 720, 900, 1080
(divide by 3)=60, 120, 180, 300, 360

For the next two values, add 360 each time, as the Cosine graph repeats every

Does this help?
4. (Original post by raheem94)

The interval is,
The interval for '3q' is

Solving will give us 3 solutions. One solution you will get from the calculator the other two solutions can be found by adding 360 and 720 to the calculator value. Now divide the solutions by 3 to get the required values of 'q'.

Below is the graph of y=cos(3q), this shows that it has 3 solution in the interval .

thanks man i solved this
but can you help me with this one
4sinq=tanq
5. (Original post by reb0xx)
thanks man i solved this
but can you help me with this one
4sinq=tanq

Remember,

Now factorise the above expression, e.g. This gives and
6. (Original post by raheem94)

Remember,

Now factorise the above expression, e.g. This gives and
why did you chose sin to be x ?
7. (Original post by reb0xx)
why did you chose sin to be x ?
I was giving you an example.
8. (Original post by raheem94)
I was giving you an example.
ok one last question
i can solve this equations using with the quadratic equation formula
this one(http://www.oncalc.com/wp-content/upl...calculator.gif)
are we allowed to solve this with a formula or by completing the square instead of factorizing it???
are we allowed to do that in the exams?
9. (Original post by reb0xx)
ok one last question
i can solve this equations using with the quadratic equation formula
this one(http://www.oncalc.com/wp-content/upl...calculator.gif)
are we allowed to solve this with a formula or by completing the square instead of factorizing it???
are we allowed to do that in the exams?
Which question are you talking about?

If the question doesn't specifies a method then you can use any method.

In your previous question, we got,

Here there is no point of using any formula or completing the square, this can easily be solved by factorisation.

So we get two equations, and

Do you get it?

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