Answer:
80 square units
Step-by-step explanation:
The area formula refers to a generic triangle ABC in which side lengths 'a' and 'b' are known and angle C is between those sides.
In the given figure, we have known side lengths of 12 and 14, and the angle between them is 72°.
Putting these numbers into the formula, we find the area to be ...
A = (1/2)(12)(14)sin(72°) ≈ 79.9 ≈ 80 . . . . square units
The area of the triangle is about 80 square units.
Given
Area of the regular pentagon is 6.9 cm².
Find out the perimeter of a regular pentagon
To proof
Formula
Area of regular pentagon is
As given in the question
area of regular pentagon = 6.9 cm²
now equating the area value with the area formula.
Now put
√5 = 2.24 ( approx)
put in the above equation
thus
a² = 4.01
a = √ 4.01
a = 2.0 cm ( approx)
As perimeter represented the sum of all sides.
i.e regular pentagon have five sides of equal length.
Thus
perimeter of the regular pentagon = 5 × side length
= 5 ×2.00
therefore the perimeter of the regular pentagon = 10cm
option c is correct
Hence proved