Which of the following describes the x-coordinates of the points on the curve cos x = e^y in the xy-plane where the curve has a horizontal tangent line?​

for this case we have by definition, if two lines are perpendicular, then the product of their slopes is -1.

then, given the following line:

so,

we are looking for m_ {2}:

then, the line is given by:

we find "b" replacing the given point:

finally, the equation is:

option c