Michael P. answered • 01/15/16

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Ryan,

You prove both postulates using the derivative (or differential) of a sum (or difference):

d(h +/- g)/dx = dh/dx +/- dg/dx

Since h and g have a relative maximum at x

_{0}, dh/dx = 0 at x=x_{0}and dg/dx = 0 at x = x_{0}.d(h +/- g)/dx = 0 +/- 0 = 0 at x=x

_{0}and, thus, h +/- g has a relative maximum at x_{0}.Michael.