trig-a level ocr

ok so here is the question:


4sin^2ϴ-1=0

here is what i try to do:
4(1-cos^2ϴ)-1=0
=4-4cos^2ϴ-1=0
= 3=4cos²ϴ
3/4=cos²ϴ

but not sure where to go from here?

What do you think? Is there an idea you've got but aren't sure whether to do it? Or are you completely stumped?

completely stuck..lol.

ok so here is the question:


4sin^2ϴ-1=0

here is what i try to do:
4(1-cos^2ϴ)-1=0
=4-4cos^2ϴ-1=0
= 3=4cos²ϴ
3/4=cos²ϴ

but not sure where to go from here?

completely stuck..lol.

Is it the $\cos^2(\theta)$ bit that's confusing you? If so, what would you do normally to get rid of a square?

I'd root it to get cosϴ = sqrt(3)/2 and then solve with whichever method you were taught (CAST diagram, drawing y = cos(x)...). p.s. examsolutions.net has a great explanation of both methods if you're not sure how to use them

Ok, first off, it's worrying that you mechanically used the sin^2 and cos^2 identity straight away without thinking about what you're trying to achieve with that.
Why are you converting the sin^2 to a cos^2? How does that make it easier?

You can simply rearrange the equation for sin^2, then obviously you need to take square roots of both sides and you should certainly be able to solve it from there.
It's funny because this is no harder that solving something like 2x^2+1=9 or sin(theta) = 2/3. It's just both together. Too many students forget everything they know when they see a problem that's slightly different to what they've done before. Maths is not being taught well in schools...

umm well cos²=1-sin²ϴ
but that then goes like this..

3/4 = 1-sin²ϴ
= 3/4 + sin²ϴ=1
sin²ϴ=4/3
and u r still left with a square lol

edit: or u could sqrt lol

umm well cos²=1-sin²ϴ
but that then goes like this..

3/4 = 1-sin²ϴ
= 3/4 + sin²ϴ=1
sin²ϴ=4/3
and u r still left with a square lol

edit: or u could sqrt lol

lol or maybe i am just dumb:/

lol or maybe i am just dumb:/
edit: btw if u just rearrange
4 sin²ϴ-1=0
u get
sin²ϴ=1/4, then u have a same problem?

See you don't even understand when to use that identity. It's just what you've been taught and you're using it without understanding what you're doing.
When doing a maths question (I hesitate to call it a 'problem', just take a second to think what you're trying to accomplish:
"I want to be able to solve for theta"
"I guess I'll need something like sin(theta)=k, which I know how to solve"
"So I'll get rid of the square by square rooting"
Please don't routinely applying formulae to a problem in hopes that it works. Understanding questions will allow you to answer a lot more and a lot more easily.

Try the square root



He is right, secondary schools teach maths to a poor standard (generally speaking).

You're right, but you could probably tone it down a little....

Plus, the style of the A-Level exams completely allow for blind memorisation of formulae and methods with virtually no understanding required. It's really quite sad, because people get the complete wrong idea of what maths is.

Trying to be as honest as possible. I think people need to be aware of what exactly they're doing wrong, even if it is a little harsh. It's only help.

ok so here is the question:


4sin^2ϴ-1=0

here is what i try to do:
4(1-cos^2ϴ)-1=0
=4-4cos^2ϴ-1=0
= 3=4cos²ϴ
3/4=cos²ϴ

but not sure where to go from here?

Indeed, I'm currently on A-level FM - which is a little better, but not much