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The graph of the parametric equations 2 x=t and y=t+1 is shown to the right. Determine whether the graph would change for each set of parametric equations. If so, how would it change?

 

a) x=sin^2(t), y=sin(t)+1

 

b) x=t^4, y=t^2+1

 

>>>> Diagram: http://i.imgur.com/p6GRAdV.png <<<<

 Apr 22, 2016

Best Answer 

 #2
avatar+118696 
+5

Thanks Chris,

 

What graphing program did you use Chris?

I played with this question too and I found it quite interesting. My results were the same as yours ofcourse.  :)

 

Here are the Desmos graphs, 

https://www.desmos.com/calculator/zcpydgu9sb

 

Ifx=t2y=t+1The restriction is x0t=±xt=y1y1=±x(y1)2=xx=(y1)2

 

As Chris said this is a sidways parabola opening in the positive direction with a vertex at (0,1)

 

Lets look at the second one

 

a) x=sin^2(t), y=sin(t)+1

The first thing I notice is that t is replaced with sin(t)

so we have 

x=sin2t0x1y=sin(t)+10y2So the domain and range are different.Butsin1(±x)=tandsin1(y1)=tsin1(±x)=sin1(y1)±x=(y1)x=(y1)2x=(y1)2So this is exactly the same as the original relation except it has different a domain and range

 Apr 22, 2016
 #1
avatar+130466 
+5

The first set of equations is

 

x = t^2   and   y = t + 1

 

Re-arranging the second one, we have y - 1  = t     and substituting this one into the first one, we have :

 

x = (y - 1)^2   which is a "sideways" parabola opening to the right with a vertex at (0, 1)

 

a) x = sin^2t    y = sint + 1

 

Rearranging the second one again, we have  sint = y - 1    and substituting this one into the first we have

 

x = (y - 1)^2 

 

However......this graph is a "restricted" version of the first one......from t = 0 to t = pi/2, the graph traces the same path from the vertex (0,1) to the point (1, 2).....then from t = pi/2 to t =pi.....it "reverses" course from (1,2) back to the vertex......from t = pi to t = 3pi/2, it traces the same path as the original graph from the vertex to the point (1, 0)...lastly, from t = 3pi/2 to 2pi......the graph again reverses course and ends back at the vertex.......this behavior is repeated infinitly

 

Here's the graph  :

 

 

b) x= t^4    y = t^2 + 1

 

Rearranging the second equation, we have y - 1 = t^2

 

Substituting this into the first equation we have the original equation, again, x = (y - 1)^2

 

However, this graph is just the [unbounded] upper half of the parabola since y is never less than 1

 

For  the interval where t ranges from (-infinity, 0), the graph traces back from the right to the point (0, 1).....when t ranges from (0, infinity), the gragh "reverses" course and traces back to the right

 

Here's the graph here traced from t = -2 to t = 2 :

 

 

cool cool cool

 Apr 22, 2016
 #2
avatar+118696 
+5
Best Answer

Thanks Chris,

 

What graphing program did you use Chris?

I played with this question too and I found it quite interesting. My results were the same as yours ofcourse.  :)

 

Here are the Desmos graphs, 

https://www.desmos.com/calculator/zcpydgu9sb

 

Ifx=t2y=t+1The restriction is x0t=±xt=y1y1=±x(y1)2=xx=(y1)2

 

As Chris said this is a sidways parabola opening in the positive direction with a vertex at (0,1)

 

Lets look at the second one

 

a) x=sin^2(t), y=sin(t)+1

The first thing I notice is that t is replaced with sin(t)

so we have 

x=sin2t0x1y=sin(t)+10y2So the domain and range are different.Butsin1(±x)=tandsin1(y1)=tsin1(±x)=sin1(y1)±x=(y1)x=(y1)2x=(y1)2So this is exactly the same as the original relation except it has different a domain and range

Melody Apr 22, 2016
 #3
avatar+130466 
+5

Thanks, Melody.....I just graphed these in WolframAlpha and took a  "screen snip"

 

 

cool cool cool

 Apr 22, 2016
 #4
avatar+118696 
0

Thanks Chris :)

 Apr 22, 2016

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