**Title:** Triangle Area: No Height?--Use the Sine

**Description:**
This lesson will lead students through a review of the proof of the Law of Sines. This proof will remind them that they can use the right triangle relationship for Sine to find the height of a triangle. They will then apply this knowledge to find the area of a triangle when given two sides and an included angle. Finally, they will be asked to find the area when no values are given. This result should produce the Area Formula for a triangle given two sides and the included angle.
This lesson results from the ALEX Resource Gap Project.
**Standard(s): **

[MA2015] PRE (9-12) 35: (+) 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. (*Apply formulas previously derived in Geometry.*) [G-SRT9] (Alabama)

**Subject:**Mathematics (9 - 12)

**Title:**Triangle Area: No Height?--Use the Sine

**Description:**This lesson will lead students through a review of the proof of the Law of Sines. This proof will remind them that they can use the right triangle relationship for Sine to find the height of a triangle. They will then apply this knowledge to find the area of a triangle when given two sides and an included angle. Finally, they will be asked to find the area when no values are given. This result should produce the Area Formula for a triangle given two sides and the included angle. This lesson results from the ALEX Resource Gap Project.