Not difficult. I talk about ideas, and the process allows children to write according to the teacher's requirements.

△AOD is similar to△ △boc because the middle side AD of the trapezoid is parallel to the side BC.

Let the height of triangle aod be x cm, then according to the similarity ratio, the height of triangle boc is 7/ 12 cm. The two add up to a trapezoidal height of 8CM.

Find the height of the triangle.

In this way, the area of the triangle can be calculated according to the formula of multiplying the base by the height.

Do your job well.

This topic examines similar triangles's judgment and nature. And the application of one-dimensional linear equation. Strong comprehensiveness.