[-/1 Points] DETAILS MY NOTES Determine the equation of the line tangent to the curve y = 7x + 2 at the point (2, 15). y [-/1 Points] DETAILS MY NOTES Math 110 Course Resources - Video Tutorial Consider the function f(x) = x4 - 8x2. Determine the number of points on the graph of y = f(x) that have a horizontal tangent line. In other words, determine the number of solutions to f'(x) = 0. Determine the values of x at which f(x) has a horizontal tangent line. Enter your answer as a comma separated list of values. The order of the values does not matter. Enter DNE if f(x) does not have any horizontal tangent lines