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C2 Trigonometry Question

Solve the equation tan θ = 2 sin θ for 0◦ ≤ θ ≤ 360◦

I got up to: Sinx/Cosx=2Sinx

the Mark scheme is attached and as always completely useless:

Screenshot 2016-06-04 at 20.40.08.png4.4KB

Screenshot 2016-06-04 at 20.40.21.png32.2KB

Reply 1

Notnek

Original post by TheAlphaParticle

Solve the equation tan θ = 2 sin θ for 0◦ ≤ θ ≤ 360◦

I got up to: Sinx/Cosx=2Sinx

the Mark scheme is attached and as always completely useless:

Multiply both sides by cos(x), move everything to the same side then take out a factor of sin(x).

Reply 2

TheAlphaParticle

Original post by notnek

Multiply both sides by cos(x), move everything to the same side then take out a factor of sin(x).

What do you mean by that?

Reply 3

the bear

^^^^ but then do not cancel out the sinx :naughty:

Reply 4

BasicMistake

Original post by TheAlphaParticle

What do you mean by that?

Multiply everything by cos(x) gives:
sin(x) = 2sin(x) cos(x)

Take over to one side:
0 = 2sin(x) cos(x) - sin(x)

Take sin(x) outside of the bracket
0 = sin(x)[2cos(x) -1]

Now you have equate each part to 0 and solve:
Let 0 = sin(x)
Let 0 = 2cos(x) -1