Question 987500
<pre>
{{{r = 4sin(theta)}}}

Always substitute for the trig functions first using 
{{{sin(theta)= y/r}}}, {{{cos(theta)=x/r}}}, {{{tan(theta)=y/x}}}.

{{{r = 4(y/r)}}}

Clear of fractions by multiplying through by r

{{{r^2 = 4y}}}

Finally replace r by {{{sqrt(x^2+y^2)}}} or in this case {{{r^2}}} by {{{x^2+y^2}}} but always 
wait till the last step to substitute for r.

{{{x^2+y^2=4y}}}

Edwin</pre>