How to calculate sin x curve graph points?

Question

I asked another question here how to plot it and I have a very good idea of how to do it now but still have some fundemental confusion.

If I have y = 5 sin 2x

I know the period is pi (2pi/2) = pi ok.
I know my amplitude is 5 ok.

Now I want to make my points to plot. So I do my x | y table and say I want x to = 0, y = 0 ok.

Now say I want to do pi/4 for one of my quarter cycles ok.

Here is where I am lost??? Do I calculate this ?

y(pi/4) = 5 sin (pi/4)
y = 5 * (sqrt2 / 2)
y = (5 sqrt2) / 2

That can't be right? My answer should be +5?
This is where I am lost and need to figure it out. I can assume that my period is 1/2 regular 2pi ok. I know it has to go up to 5.

Here is where I even get more confused

pi / (3/4) gives me 3pi/4 right?

Well sin 3pi/4 = sqrt2/2 again... How is this -5???

I know I'm missing something real basic here but it is making it impossible for me to do this work so any help please!!! make it for an idiot to understand :)
thanks

Answer 1

y(pi/4)=5sin(2(pi/4)) = 5sin(pi/2) = 5

Answer 2

you need your max and your min which will be 1 and -1 since there is no vertical shift. then since the period is pi you start with pi and then go a pi every next point with the min and the max

Answer 3

y = 5 sin 2x
so y(pi/4) = 5 sin (pi/2) = 5
You just forgot to double the angle.