Write the equation of a sine or cosine function to describe the graph.

D is the midline, this refers to the midpoint of the highest y value and lowest y value. Some textbooks call it the vertical translations but it is the same thing.

A is the amplitude. The amplitude is the distance from the midline to the highest y value. Some distance is non negative, the formula for the amplitude is

[tex] |a| [/tex]

The period is how often the wave repeats itself on a interval.

Period can't be negative so the formula for period is

[tex] \frac{2 \pi}{ |b| } [/tex]

To find the period, look at the extreme points.

The phase shift tells us if the sinusoid have been shifted to the right or left. The formula for the phase shift

[tex]bx + c = 0[/tex]

Solving for x gives us

[tex]x = \frac{ - c}{b} [/tex]

If our x is negative, we have a phase shift to the right

If our x is Positve, we have a phase shift to the left.

Let solve this equation, Let use Sine since sin(0)=0,

The smallest y value here is 0, and the highest is 2, so the amplitude is 1.

[tex]d = 1[/tex]

Next, the distance from the max to the midline is 1, as well the min to the midline is also 1.

So

[tex]a = 1[/tex]

We have minimum at 0, and 8, so our period is 8.

[tex] \frac{2\pi}{b} = 8[/tex]

Solve for b,

[tex] \frac{\pi}{4} = b[/tex]

Plug this in the equation.

[tex]1 \sin( \frac{\pi}{4} x) + [/tex]

[tex]y = \sin( \frac{\pi}{4} x) + 1[/tex]

The graph passes through (4,2) so let see if that holds true for our equation

[tex]2 = \sin( \frac{\pi}{4} (4)) + 1[/tex]

[tex]2 = \sin(\pi) + 1[/tex]

[tex]2 = 0 + 1[/tex]

[tex]2 = 1[/tex]

This doesn't hold true, so we must have a phase shift

Notice that

[tex] \sin( \frac{\pi}{2} ) = 1[/tex]

So if we shift this pi/2 to the right, we can get our equation to be true.

[tex]y = \sin( \frac{\pi}{4} x - \frac{\pi}{2} ) + 1[/tex]

This equation works so our equation is

[tex]y = \sin( \frac{\pi}{4} x - \frac{\pi}{2} ) + 1[/tex]