2. Determine the numbers x between 0 and 2pi where the tangent line to the curve is horizontal. Need help ASAP

Assuming the curve is

y = cos(x) - √3 sin(x)

differentiate once to get dy/dx, which gives the slope of the tangent line to y at some point x. The derivative is

dy/dx = -sin(x) - √3 cos(x)

The tangent line is horizontal when the derivative is 0, so you end up having to solve

-sin(x) - √3 cos(x) = 0

sin(x) = -√3 cos(x)

sin(x)/cos(x) = tan(x) = -√3

x = arctan(-√3) + nπ

(where n is an integer)

x = -arctan(√3) + nπ

x = -π/3 + nπ

You get two solutions in the interval [0, 2π] when n = 1 and n = 2, for which

x = 2π/3   or   x = 5π/3