Measure the length of each of the trapezoid's bases. Or you may be given this information. Add the result together to obtain the sum of the length of the bases.
Measure the distance of a vertical line (the height of trapezoid) that extends between the two base lines on the trapezoid. Again, you may be given this information in the problem.
Multiply the sum of the trapezoid bases by the height of the trapezoid. Divide the result by 2 to obtain the trapezoid's area.
Verify that area for a trapezoid that has one base with a length of 2, another base with a length of 3 and a height with a length of 5 is 12.5. Add 2 plus 3 to obtain 5 and multiply this result by the height to obtain 25. Then divide the result by 2 to obtain the correct result: 12.5 square units.
Use the trapezoid area calculator at the "Trapezoid Area Calculator" link in Resources to check your math and procedures.
Write down the variables given for the trapezoid problem. Suppose you're given a trapezoid area of 3, a lower base length of 2 and an upper base length of 1 for this problem, in which you must solve for height.
Substitute these variables into the trapezoid area formula:
Area = height * (base1 + base2)/2
So you would obtain 3 = height*(1 + 2)/2. Multiply both sides of the equation by 2 to obtain 6 = 3*height. Divide both sides of the equation by 3 to obtain a height of 2.
Verify that 2 is the answer by substituting the height calculated and the variables given back into the area formula. So area = (2)*(1 + 2)/2. Simplify the expression to A = (1 + 2) by canceling the twos. Add the result to obtain an area of 3.
You can conclude that 2 is the correct answer for the height because the area given for the original problem was also 3.