Inputting this function of x into the nth Chebyshev polynomial of the first kind yields this function of nx. This function equals the average of e to the ix and e to the minus ix, and the hyperbolic form of this function is the average (10[1])of e to the x and e to the minus x. The first two terms of this function’s Taylor series are one and minus (10[2])one-half (10[1])x-squared. For a complex number of modulus one, this function of the argument is the number’s real part. (10[2]-5[1])Pythagoras’ theorem is a special case of a law named after this function. (10[1])The reciprocal (10[1])of this function is secant. For 10 points, name this trigonometric function that equals adjacent over hypotenuse in a right triangle. ■END■