Proof that sin(-θ) = – sin(θ), cos(-θ) = cos(θ), and tan(-θ) = -tan(θ)

In order to understand the proof below, you must have a prior knowledge about circular functions. The proof also uses symmetry which is I think quite basic for high schools students. The basic idea is that the point  is symmetric with the point with respect to the axis. The angles and are rotations with the positive x-axis as the initial […]
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Deriving the Area of a Triangle using Trigonometry

The area of the triangle is half the product of its base and altitude. In the figure below for instance, the area  of the two triangles with base and altitude is given by the formula .   In this post, we derive the area of a triangle using trigonometry In particular, we want to compute […]
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