Question 567036
<pre>
{{{sqrt(9-x^2)}}}

{{{sqrt(9-(3sin(x))^2)}}}  <-- notice that the 3 must be inside parentheses
                as a coefficient of sin(x). That was an
                error you made.  That is, the 3 is squared
                along with the sin(x).  The way you had it
                the 3 was not squared as it should have been.  

{{{sqrt(9-3^2sin^2(x))}}}

{{{sqrt(9-9sin^2(x))}}}

{{{sqrt(9(1-sin^2(x)))}}}

{{{sqrt(9)sqrt(1-sin^2(x))}}}

{{{3sqrt(1-sin^2(x))}}}

{{{3sqrt(cos^2(x))}}}

Since the cosine is sometimes negative, but
the square root of its square when written with a
radical is never negative.  Therefore we must
put absolute value bars around the square root to
prevent it from ever being negative:

Answer {{{3abs(cos(x))}}}

Edwin</pre>