Thread: Equations involving trig identities/formulae

I just need someone to guide me on how to get started on these. Generally I change the identities I spot into its equivalent, before proceeding to get lost.

Anyway, hopefully I can format these questions correctly:

a) 2sinx -cotx -cscx = 0

b) sin2x + cosx = 0

c) sinx - cosx = 0

Originally Posted by Cheagles

I just need someone to guide me on how to get started on these. Generally I change the identities I spot into its equivalent, before proceeding to get lost.

Anyway, hopefully I can format these questions correctly:

a) 2sinx -cotx -cscx = 0

b) sin2x + cosx = 0

c) sinx - cosx = 0

For number 1, try multiplying all by sinx, and then using . For number two, use the double angle formula for sin2x, do you know it? Oh, and for number 3 I'd suggest multiplying by and see what you can do from there. Remember, you're just looking for ways to reduce to a single identity.

1)

2sinx -cotx -cscx = 0

2sinx - cosx/sinx - 1/sinx =







Now its simple

2) sin2x + cosx = 0

Its simple quadratic equation in cos x


3) sinx - cosx = 0

Thank you, JeWiSh and arpitagarwal82. I just got done with the homework packet and ended up with only two mistakes, that I'm still trying to wrap my head around:

1) tanx + secx = 1

and

2) sin2x + cosx = 0 (I realize I already asked this, but I got it wrong. After applying the quadratic formula, I ended up with 1/2 and -1. I looked at the unit circle and got 60, 180, and 300 degrees. Where did I screw up?)

Thanks again.