How to Compute Area of Triangle (side angle side)

The area of a triangle can be calculated if you know the length of two sides and the angle between them. This formula for calculating the area of a triangle uses the sine trig function.

Things You'll Need

• scientific calculator or trig table

Instructions

1. 

   As our example, let's take a triangle with side lengths 6 and 11 with an angle of 70 degrees between. The first step is to multiply 6 and 11 and then divide the product by 2.

   (6)(11) = 66, and 66/2 = 33.

2. The next step is to use a calculator or trig table to figure the sine of 70 degrees. There are three main trigonometric functions, sine, cosine, and tangent. Sine(70) is .9396.

   Now multiply .9396 times the number you computed in step 1. (.9396)(33) = 31.0068. So the area of the triangle is essentially 31 square units

3. For a triangle with side lengths of A and B and an angle of x degrees between them, the formula for the area of the triangle is (1/2)ABsin(x).