Triangle Area by Subtracting From a Rectangle

Start with the sheets on acute and right triangles, then move to obtuse triangles and trapezoids. Use the mixed sheets as review and the answer keys for quick checking.

Box each triangle in a grid rectangle and subtract three outer right triangles to find its area. The directions on the page read: Box each triangle in the smallest grid rectangle. In the table, write the areas of the rectangle and the 3 outer right triangles in any order. Subtract to get the triangle's area in square units. An answer key is included.

Yes, both. We made it for 7th grade geometry, and it works the same at home or at school. At home, a student can work through it alone and then go over it with you, which shows quickly what is solid and what needs another look. In class it works as independent practice, homework or a warm-up, and you can print one copy or a full set.

Multiply the base by the height, then divide by 2. The height meets the base at a right angle, and in an obtuse triangle it can fall outside the triangle.

Add the two parallel bases, multiply by the height and divide by 2. The Trapezoid Area With Decimal Measures worksheet practices this with decimal lengths.

Write an equation from the area formula, put in the known measures and solve. The Missing Height of Acute Triangles worksheet gives the area and base and asks for h.

Yes. All 20 worksheets in this group have answer keys.