The apothem of a regular quadrangular pyramid is 6, and the angle between the planes of the base
The apothem of a regular quadrangular pyramid is 6, and the angle between the planes of the base and the side face is 30 °. Find the volume of the pyramid.
Let’s draw the diagonals of the square at the base of the pyramid and connect the point O with the exact H apothem. the linear angle KNO is equal to the dihedral angle between the side face and the base of the pyramid, the angle KHO = 30. Then in a right-angled triangle KOH the leg KO lies opposite the angle 30, and therefore KO = KH / 2 = 6/2 = 3 cm.
CosKHO = OH / KH.
OH = KH * CosKHO = 3 * Cos30 = 3 * √3 / 2.
Since OH is the middle line of the ACD triangle, then AD = 2 * OH = 2 * 3 * √3 / 2 = 3 * √3 cm.
Determine the area of the base of the pyramid.
Sbn = АD ^ 2 = 9 * 3 = 27 cm2.
Then V = Sosn * KO / 3 = 27 * 3/3 = 27 cm3.
Answer: The volume of the pyramid is 27 cm3.