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# C3 trig question watch

1. How to do you solve

2sinxcosx = - sinx

In the range 0degrees </= x </= 360 degrees?
2. Sin x is on both sides so that can be removed by dividing.
3. (Original post by Phoebus Apollo)
How to do you solve

2sinxcosx = - sinx

In the range 0degrees </= x </= 360 degrees?
Rearrange to get = 0 and factorise. Once it's factorised think about how you would solve a factorised quadratic.
4. (Original post by Vikingninja)
Sin x is on both sides so that can be removed by dividing.
Dividing results in loss of solutions. Always factorise.

What have you tried, OP?
5. (Original post by Phoebus Apollo)
How to do you solve

2sinxcosx = - sinx

In the range 0degrees </= x </= 360 degrees?
You need to get all x terms on one side so the other side =0, and then factorise to solve, setting each factor which can =0 to 0. If this is confusing, tell me.
6. (Original post by Vikingninja)
Sin x is on both sides so that can be removed by dividing.
Doing so will lose a root. You can only divide both sides of an equation by something if you know that something is non-zero.
7. (Original post by Vikingninja)
Sin x is on both sides so that can be removed by dividing.
You lose a solution if you divide by sinx

Damn, I got beaten
8. Roughly like this
2sinxcosx + sinx = 0
sinx(2cosx +1) = 0
sinx= 0 and 2cosx+1=0

then just solve as normal
9. (Original post by Vikingninja)
Sin x is on both sides so that can be removed by dividing.
But don't forget sinx = 0...
I did that once, my C2 result still haunts me
10. (Original post by Vikingninja)
Sin x is on both sides so that can be removed by dividing.
I hope you're joking.
11. (Original post by SeanFM)
Dividing results in loss of solutions. Always factorise.

What have you tried, OP?
I made up the question because I wanted to see whether i should divide or factorise in that situation. Thanks for your reply!
By the way If you had:
2sinx/cost = -1/cosx and you cross multiplied, what would you do then?
12. (Original post by Phoebus Apollo)
I made up the question because I wanted to see whether i should divide or factorise in that situation. Thanks for your reply!
By the way If you had:
2sinx/cost = -1/cosx and you cross multiplied, what would you do then?
Assuming that's cosx and not cost, I'd rearrange that to make it equal to 0 and see that it doesn't matter what cosx is as it is on the denominator.
13. (Original post by SeanFM)
Assuming that's cosx and not cost, I'd rearrange that to make it equal to 0 and see that it doesn't matter what cosx is as it is on the denominator.
So you would only get sinx = -1/2?
14. (Original post by Phoebus Apollo)
So you would only get sinx = -1/2?
Yes.

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