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