find equation of a tangent line to y=x^3-5x+6 at the point where x=2

Now this is the last one. These are basis and you should try them.

dy/dx = slope = m = 3x^2 -5
at x = 2, m = 12-5 = 7
so line is of form
y = 7x+b
at x = 2, y = 8-10+6 = 4
so tangent at point (2,4)
4 = 14+b
so
b = -10
so
y = 7 x -10