Math Is Fun Forum

djbip

Member

Registered: 2008-03-27

Posts: 13

A few trig questions

1)  2cosx - 4sin²x=0

I found cosx = 0 and sinx= -0.25. Is it right?

2)  sinx + 1 - 2cos²x=0

3) cos²x + sinx +1=0

JaneFairfax

Member

Registered: 2007-02-23

Posts: 6,868

Re: A few trig questions

For the first question, use the identity

; for the other two questions, use

.

This should give you a quadratic in cos(x) for #1 and in sin(x) for #2 and #3, which you should be able to solve.

djbip

Member

Registered: 2008-03-27

Posts: 13

Re: A few trig questions

Can someone please solve them for me?

I knew about the identity before I posted. I just don't know if I got the right results.
I'm not asking about the method, I asking about the right result.

Last edited by djbip (2008-05-29 09:02:55)

Dragonshade

Member

Registered: 2008-01-16

Posts: 147

Re: A few trig questions

For the second one,

Last edited by Dragonshade (2008-05-29 10:27:28)

iamthepro

Member

Registered: 2008-06-01

Posts: 1

Re: A few trig questions

If u are unsure u can sub back your answer see if u get a answer close to zero.
(most likely won't be zero since theres some rounding up and down)

esatpllana

Member

Registered: 2007-11-22

Posts: 12

Re: A few trig questions

3) cos²x + sinx +1=0

now we have a quadtratic equation

sorry if have mistake I am newer in Trigonometry

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