May 15, 2015

Students prove that the area of a triangle is one-half times the product of two side lengths times the sine of the included angle and solve problems using this formula.

Students find the area of an isosceles triangle given the base length and the measure of one angle.

Teacher and Student versions of full lesson from engageNY

- Mathematics > General
- Mathematics > Geometry

- Grade 9
- Grade 10

Make sense of problems and persevere in solving them.

Reason abstractly and quantitatively.

Use appropriate tools strategically.

Attend to precision.

Look for and make use of structure.

(+) Derive the formula A = 1/2 ab sin(C) for the area of a triangle by drawing an auxiliary line from a vertex perpendicular to the opposite side.