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nirvana33 [79]
3 years ago
9

Prove algebraically that r = 10/2+2sinTheta is a parabola

Mathematics
1 answer:
Xelga [282]3 years ago
4 0

Answer:

y =  -  \frac{ 1 }{10} {x}^{2}   +  \frac{5}{2}

Step-by-step explanation:

We want to prove algebraically that:

r =  \frac{10}{2 + 2 \sin \theta}

is a parabola.

We use the relations

{r}^{2}  =  {x}^{2}  +  {y}^{2}

and

y = r \sin \theta

Before we substitute, let us rewrite the equation to get:

r(2 + 2 \sin \theta) = 10

Or

r(1+  \sin \theta) = 5

Expand :

r+  r\sin \theta= 5

We now substitute to get:

\sqrt{ {x}^{2}  +  {y}^{2} }  + y = 5

This means that:

\sqrt{ {x}^{2}  +  {y}^{2} }=5 - y

Square:

{x}^{2}  +  {y}^{2} =(5 - y)^{2}

Expand:

{x}^{2}  +  {y}^{2} =25 - 10y +  {y}^{2}

{x}^{2}  =25 - 10y

{x}^{2}  - 25 =  - 10y

y =  -  \frac{ {x}^{2} }{10}  +  \frac{5}{2}

This is a parabola (0,2.5) and turns upside down.

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a. The general equation for a circle centered at (a,b) with radius r is

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We know the circle passes through the origin. This means that the equation above holds for x=0 and y=0. The distance between any point on the circle and its center is the radius, so we can use this fact to determine r:

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