Exponent[expr, form] gives the maximum power with which form appears in the expanded form of expr.
Exponent[expr, form, h] applies h to the set of exponents with which form appears in expr.
Example: Exponent[x^2 + a x^3, x]. The default taken for h is Max. Example: Exponent[x^2 + a x^3, x, List].
form can be a product of terms.
Exponent works whether or not expr is explicitly given in expanded form. See The Mathematica Book on the web: Section 1.4.7 and Section 3.3.2. See also: Coefficient, Cases, IntegerExponent.
Exponent[expr, form] gives the maximum power with which form appears in the expanded form of expr. 
. 
. 