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 Area of a Triangle Part II Unit 1 > Lesson 4 of 8

Example 1: Find the area of an acute triangle with a base of 15 inches and a height of 4 inches.
Solution:
= · (15 in) · (4 in)
= · (60 in2)
= 30 in2

Example 2: Find the area of a right triangle with a base of 6 centimeters and a height of 9 centimeters.
Solution:
= · (6 cm) · (9 cm)
= · (54 cm2)
= 27 cm2

Example 3: Find the area of an obtuse triangle with a base of 5 inches and a height of 8 inches.
Solution:
= · (5 in) · (8 in)
= · (40 in2)
= 20 in2

Example 4: The area of a triangular-shaped mat is 18 square feet and the base is 3 feet. Find the height. (Note: The triangle in the illustration to the right is NOT drawn to scale.)
Solution: In this example, we are given the area of a triangle and one dimension, and we are asked to work backwards to find the other dimension.
18 ft2 = · (3 ft) ·
Multiplying both sides of the equation by 2, we get:
36 ft2 = (3 ft) ·
Dividing both sides of the equation by 3 ft, we get:
12 ft =
Commuting this equation, we get:
= 12 ft

Summary: Given the base and the height of a triangle, we can find the area. Given the area and either the base or the height of a triangle, we can find the other dimension. The formula for area of a triangle is:

 or where is the base, is the height