The law of cosines, Trig 11?

Question

Ok, last one guys ^^

Thanks for all your help so far!

Ok, here it is:

A sail that is in the shape of an isosceles triangle has a vertex angle of 38 degrees.

The angle is included by two sides, each measuring 20 ft. Find the area of the sail.

Please refreash my memory on what an isoceles triangle and wish me luck on my test tommorow! I'm going to need it!!!

Thanks again everyone ^0^

Answer 1

Consider triangle ABC
AB = AC = 20
BC = base = b
Height = h

Angle BAC = 38°
Angle ABC = Angle ACB = 71°
b = 20 cos 71°
h = 20 sin 71°

Area = (1/2) b h
Area = (1/2) (20 cos 71°)( 20 sin 71°) ft ²
Area = 61.6 ft ²

Answer 2

An isosceles triangle is one with 2 equal sides and 2 equal angles. Draw your diagram and you'll see that your triangle will have two sides of 20ft and one unknown side. The angles will be 38 and 71 and 71 (add to 180).
To find the area of the sail is easy 1/2 x 20 x 20 x sin 38 =
123.13 sq feet.No need for cosine rule.

Answer 3

isoceles triangle is triangle with 2 sides equal
1/2*20*20*sin38
200sin38
123.132