Help me please!

Solve the equation

3 cosec x + 8 cos x = 0

for x in the interval 0 < x < 180, giving your answers to 1 decimal place.

I have no idea why I find this question so hard!!! It's only question 1 on the paper - lame, huh? tbh, I'll find it easy once I've got going, but I don't know where to start. Any suggestions??? ...At all?

Reply 1

Jelkin

OP

17

Solve the equation

3 cosec x + 8 cos x = 0

for x in the interval 0 < x < 180, giving your answers to 1 decimal place.

I have no idea why I find this question so hard!!! It's only question 1 on the paper - lame, huh? tbh, I'll find it easy once I've got going, but I don't know where to start. Any suggestions??? ...At all?

Reply 2

Gaz031

15

Jelkin

Solve the equation

3 cosec x + 8 cos x = 0

for x in the interval 0 < x < 180, giving your answers to 1 decimal place.

I have no idea why I find this question so hard!!! It's only question 1 on the paper - lame, huh? tbh, I'll find it easy once I've got going, but I don't know where to start. Any suggestions??? ...At all?

3/sinx+8cox=0
3+8sinxcosx=0
8sinxcosx=-3
4sin2x=-3
sin2x=-3/4.
Solve to find values of 2x and hence values of x in the required interval [Remember the CAST diagram].
If you ever need maths help you'll probably get more replies in the maths forum in the academic help section.

Reply 3

Jelkin

OP

17

I'm sorry to post this on this board but no one is on the maths board and I need help!

Solve the equation

3 cosec x + 8 cos x = 0

for x in the interval 0 < x < 180, giving your answers to 1 decimal place.

I have no idea why I find this question so hard!!! It's only question 1 on the paper - lame, huh? tbh, I'll find it easy once I've got going, but I don't know where to start. Any suggestions??? ...At all?

Reply 4

Jelkin

OP

17

Thanks! I did try posting it in the Maths forum but no one has posted anything on there in ages so I didn't think I'd get a reply!

Reply 5

Gaz031

15

Jelkin

Thanks! I did try posting it in the Maths forum but no one has posted anything on there in ages so I didn't think I'd get a reply!

Np. I meant this one: http://www.thestudentroom.co.uk/f56.html

Reply 6

m:)ckel

14

3cosec x + 8cos x = 0
3/sinx + 8cosx = 0
3 + 8sinxcosx = 0 . . . (multiplied through by sinx)
3 + 4(2sinxcosx) = 0
3 + 4sin2x = 0
sin2x = -3/4

2x = -48.6 , 228.6 , 311.4 degrees

x = 114.3 , 155.7 degrees {the other one is outside the range}

Oh, and I'm surprised no-one else in Maths has answered this :s