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Feb 11, 2020
 #2
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Feb 11, 2020
 #11
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Equation: y = -2 cos 4 x + 3

 

Desmos Graph: https://www.desmos.com/calculator/e5jilhrvfk

 

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- Questions -

 

1) Midline: y = 3                    yes

 

2) Topline: 5                           y=5   It is a line!

 

3) Bottom Line: 1                      y=1

 

4) Wavelength: π/2                          2pi/4 = pi/2      GOOD

 

5) Quarter Of The Wavelength: π/4     X     one quarter of pi/2   IS NOT pi/4           \(\frac{1}{4}*\frac{\pi}{2}=\frac{\pi}{8}\)

 

6) What would be sensible points for the x-axis? π/4, 3π/4, 5π/4, 7π/4, 9π/4 (?)

pi/8, 2pi/8=pi/4, 3pi/8, 4pi/8=pi/2   etc         

 

7) Will it start on the midline, above or under, why? ​It will start below the midline because it is a cos graph.  

NO   Sin graphs start in the middle because sin0=0

+cos0=1    -cos0=-1      This equation has the minus sign so it will start (cross the y axis) at the bottom.

 

8) Will is start going down or going up, why?​ It has begun at its lowest point as a cos graph and will begin upwards. 

Up because it is is already at the bottom. 

 

9) y-intercept: 1     YES    (this is the bottom!)

 

10) Plot 4 (or 5) points in advance just by knowing what the properties of the graph will be.

 I mean maxima, minima, and points on the midline: (π/8, 3), (3π/8, 3), (5π/8, 3), (7π/8, 3), (9π/8, 3) [Or] (π/4, 5), (3π/4, 5) [Etc]      (0,1)

 

11) Graph it from x = 0 to x = Wavelength: 

 

12) What is the first maxima? (π/4, 5)

 

13) What is the first minima? (π/2, 1)

 

14) What are points on the midline? (π/8, 3), (3π/8, 3), (5π/8, 3), (7π/8, 3), (9π/8, 3) (?)   

Good but I also wanted the ones at the top and bottom (0,-1), pi/4,5), (pi/2,-1)

Look at the graph.

 

Hopefully these are all correct!     You are getting there :)

You need to do a freehand sketch as you answer the questions. They will complement each other and make it easier.

 

Here is a graph with a better step on the x axis. I have made the x step equal to one quarter of a wave.

https://www.desmos.com/calculator/lh4pzfxeja

I have only added the shaded green so that you can easily see one wavelength.

See how it starts at the bottom.

when x=0   y=-2cos(4*0)+3 = -2*1+3 = 1   (which is at the bottom of the wave)

 

 

Feb 11, 2020

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