Question

A square pyramid has base area 64 square centimeters. The surface area of this pyramid is 224 square centimeters. Find the height (h) to the nearest tenth of a centimeter. Pyramid height=_____cm.

Answer 1

Answer:

$h \approx 12.7\,cm$

Step-by-step explanation:

The side of the square base is:

$l = \sqrt{64\,cm^{2}}$

$l = 8\,cm$

The formula for the surface area of the pyramid is:

$A_{s} = \frac{1}{2}\cdot (3\cdot l)\cdot \sqrt{0.25\cdot l^{2}+h^{2}} + l^{2}$

The height is cleared in the previous expression:

$A_{s} - l^{2} = \frac{3}{2}\cdot l\cdot \sqrt{0.25\cdot l^{2}+h^{2}}$

$\frac{2}{3}\cdot \frac{A_{s}-l^{2}}{l} = \sqrt{0.25\cdot l^{2} + h^{2}}$

$\frac{4}{9}\cdot \left(\frac{A_{s}-l^{2}}{l} \right)^{2} = \frac{1}{4} \cdot l^{2} + h^{2}$

$h = \sqrt{\frac{4}{9}\cdot \left(\frac{A_{s}-l^{2}}{l} \right)^{2} - \frac{1}{4}\cdot l^{2}}$

$h = \sqrt{\frac{4}{9}\cdot \left[\frac{224\,cm^{2}-(8\,cm)^{2}}{8\,cm}\right]^{2}-\frac{1}{4}\cdot (8\,cm)^{2} }$

$h \approx 12.7\,cm$