What is the missing number?
1 answer:
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A pyramid is regular if its base is a regular polygon, that is a polygon with equal sides and angle measures.
(and the lateral edges of the pyramid are also equal to each other)
Thus a regular rectangular pyramid is a regular pyramid with a square base, of side length say x.
The lateral faces are equilateral triangles of side length x.
The lateral surface area is 72 cm^2, thus the area of one face is 72/4=36/2=18 cm^2.
now we need to find x. Consider the picture attached, showing one lateral face of the pyramid.
by the Pythagorean theorem:
thus,
thus:
(cm^2)
but
is exactly the base area, since the base is a square of sidelength = x cm.
So, the total surface area = base area + lateral area =
cm^2
Answer: cm^2
(and the lateral edges of the pyramid are also equal to each other)
Thus a regular rectangular pyramid is a regular pyramid with a square base, of side length say x.
The lateral faces are equilateral triangles of side length x.
The lateral surface area is 72 cm^2, thus the area of one face is 72/4=36/2=18 cm^2.
now we need to find x. Consider the picture attached, showing one lateral face of the pyramid.
by the Pythagorean theorem:
thus,
thus:
but
So, the total surface area = base area + lateral area =
Answer: