# Math Help - Trig Identity Homework Help Please!

1. ## Trig Identity Homework Help Please!

I'm having trouble with some trig hwk problems, these are the specific ones. If anyone can help me i would appreciate it. Btw, this is my first post on here, heard about the forum from a friend, hopefully people can help me a lot on here! I need all the extra help i can get! Thanks!

3) If sinA=-5/13 with A in QIII, find the exact value of:

a) cos A/2(half-angle formula) b) sin2A(Double-Angle formula)

2cos²x-5sinx-4=0

8) Find all solutions Θ for 0°≤Θ<360° NOT 0°≤Θ≤360°.

√3sinΘ+cosΘ=1

2. did i post too many problems at once?

3. ok i made the list smaller because i was able to get some worked out. nobody has time to help? i need this for tommorow

4. yo moderator, help a newb out! Im falling into the darkness of the sinx world!!!!!!!

5. ## Re :

Originally Posted by norcal1.8t
I'm having trouble with some trig hwk problems, these are the specific ones. If anyone can help me i would appreciate it. Btw, this is my first post on here, heard about the forum from a friend, hopefully people can help me a lot on here! I need all the extra help i can get! Thanks!

3) If sinA=-5/13 with A in QIII, find the exact value of:

a) cos A/2(half-angle formula) b) sin2A(Double-Angle formula)

2cos²x-5sinx-4=0

8) Find all solutions Θ for 0°≤Θ<360° NOT 0°≤Θ≤360°.

√3sinΘ+cosΘ=1

(1) $cos2A=2cos^2 A-1$
$cosA=2cos^2(A/2)-1$
cos(A/2)=SQRT((cosA+1)/2 )
note that cos A = -12/13
sin2A= 2sinAcosA

(2)Remember cos^2 x + sin^2 x = 1
2 ( 1-sin^2 X) - 5sin X -4 = 0
i guess you can work this out

6. ## Re :

Originally Posted by norcal1.8t
8) Find all solutions Θ for 0°≤Θ<360° NOT 0°≤Θ≤360°.

√3sinΘ+cosΘ=1
(√3sinΘ+cosΘ)^2=(1)^2
3sin^2Θ+2SQRT3sinΘcosΘ+cos^2Θ=1
3sin^2Θ+2SQRT3sinΘcosΘ=sin^2Θ
2sin^2Θ(sinΘ+SQRT3cosΘ)=0
nvm , then solve for Θ .

7. phew, thanks a lot of, that saved me lots of trouble! Appreciate it!