A right circular cone has base radius 9 and height 15. It is sliced by a plane passing through the apex and perpendicular to the base (through the center), as shown by the dashed lines. What shape is this cross section, and what is its area?
AAn isosceles triangle with base 18 and height equal to the slant height 17.49; area = 157.44 sq. units
BAn isosceles triangle with base 18 and height 15; area = 270 sq. units
CAn isosceles triangle with base 18 and height 15; area = 135 sq. units
DA circle with radius 9; this cross section has no defined area formula
Explanation
A plane through the apex and the center of the base creates an isosceles triangle whose base is the cone's diameter (2×9 = 18) and whose height is the cone's actual height (15), NOT the slant height. Area = ½ × 18 × 15 = 135 sq. units.
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