That law is a generalization of the Pythagorean theorem.
This function has a fixed point known as the Dottie number equal to roughly 0.74. This function names a version of the discrete Fourier transform that uses only real numbers, and the Fourier series of an even function has only terms proportional to this function. Its Taylor series has "2 n factorial" in the denominators and begins "one minus one-half x squared." One law named for this function has a term in which it is multiplied by twice the product of side lengths a and b. That law is a generalization of the Pythagorean theorem. For 10 points, name this trigonometric function which for an angle in a right triangle is the adjacent side length over hypotenuse length.
This function has a fixed point known as the Dottie number equal to roughly 0.74.
cosine