<PRE><B>Question 1195527</B>
PQR is an isosceles triangle with a base of 18 cm and sides of 15 cm and is inscribed in a circle with its vertices touching the circumference of the circle. The radius, in centimetres, of the circle is?
:
draw this out, assume the base of the triangle (18cm) is below the center
Find the height of the triangle using pythag;
h goes thru the center. 
h = {{{sqrt(15^2 - 9^2)}}}
h = 12 cm
:
let x = dist from the center to the center of the base, then we have
r = 12 - x
drawn a right triangle using the radius (r), x and half the base (9), find r
r = {{{sqrt(x^2 + 9^2)}}}
:
r = r therefore
{{{sqrt(x^2+9^2)}}} = 12 - x
square both sides
{{{x^2 + 9^2  = 144 - 24x + x^2}}}
x^2 drops out
81 = 144 - 24x
24x = 144 - 81
24x = 63
x = 63/24
x = 2.625
find the radius
r = 12 - 2.625
r = 9.325
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