If we draw the graph of that on polar graph paper. we make
a table of points:
q | r
0院0.00
15院1.55
30院3.00
45院4.24
60院5.20
75院5.80
90院6.00
105院5.80
120院5.20
135院4.24
150院3.00
165院1.55
180院0.00
We get this circle:
When changing from one form to the other always draw this first:
We substitute for the sine first.
Looking at the triangle and remembering that
so substitute for first
Multiply both sides by r
Now use the Pythagorean theorem to substitute
for <-- answer
As a check let's graph it.
Get it in standard form:
Write x as (x-0)
Complethe square:
take half or -6, get -3
Square it, get 9
Add 9 to both sides:
Factor the trinomial in y:
That's a circle with center (0,3) and radius 3:
It graphs as the same circle, so we are right.
Edwin