For ten points, give this even trigonometric function, which in a right triangle is equal to adjacent over hypotenuse, and whose square is equal to one minus sine-squared.
The sum of this function applied to each of the three angles of a triangle gives one plus the inradius over circumradius. This function's hyperbolic analogue is equal to e to the x plus e to the negative x all over two, and is the equation for a catenary curve. This function of theta gives the real part of e to the power of i times theta, and the (*) dot product of two unit vectors is equal to this function of the angle between them. For ten points, give this even trigonometric function, which in a right triangle is equal to adjacent over hypotenuse, and whose square is equal to one minus sine-squared.
The sum of this function applied to each of the three angles of a triangle gives one plus the inradius over circumradius.
cosine (accept cosh or hyperbolic cosine after that clue is read) &lt;MS&gt;