Make: Robotic Arms

55Chapter 3: Inverse Kinematics for 2D Movement

Normally, when using sin, cos, or tan, you are

given some combination of one of the angles of

the triangle and a few of the sides. As we saw

in the previous example, with the use of arctan,

we can determine the value of an angle in the

triangle as long as we know the lengths of at

least two sides of the triangle. This can be useful,

but there’s a catch: This is true only with right

triangles, such as our lower triangle.

The upper triangle we’ve created is not a right

triangle. Thanks to the law of cosines, we can still

solve for the angles within the non–right triangle,

but in order to do so, we ...