Geometry: What is the height of a solid pyramid So the question is OPQRS is a right pyramid whose base is a square of sides 12 cm each. Given that the the slant height of the pyramid is 15cm. And now I need to find the Height of the pyramid. 
I did my equation like this:
QR 1/2 = 6cm
HEIGHT^2 = 6^2+12^2
                   = 180
So height is root over 180 and thus I got 13.4 cm. But the answer at the back of my book says 13.7cm. Can anyone tell me what or why my answer is wrong?

The correct calculation is $\sqrt{15^2-(\frac{12}{2})^2}=\sqrt{189}=13,748$
