You are Here: Home >< Maths

# c2 trigonometrical identities and simple equestions Watch

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?

Updated: April 7, 2012
TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Today on TSR

### Grade boundaries not out until results day

What does this mean for you?

Poll
Useful resources

## Make your revision easier

### Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

### How to use LaTex

Writing equations the easy way

### Study habits of A* students

Top tips from students who have already aced their exams

Can you help? Study help unanswered threads

## Groups associated with this forum:

View associated groups
Study resources

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.