The base of a regular right pyramid is an isosceles triangle with equal sides of 25 cm and a base of 30 cm. The slant height of the pyramid is 40 cm. Find the total surface area of the pyramid.
Show answer & explanation
Correct answer: C
Explanation
Given:
Base = isosceles triangle
Equal sides = 25 cm
Base = 30 cm
Slant height of the pyramid = 40 cm
Formula:
Total surface area of the pyramid = Base area + Lateral surface area
Height of the base triangle = √(25 × 25 − 15 × 15) = 20 cm
Base area = (1/2) × 30 × 20 = 300 cm²
Lateral surface area = (1/2) × (25 + 25 + 30) × 40 = 1600 cm²
Total surface area = 300 + 1600 = 1900 cm²