Find the number of terms in the expansion of (x+y+z+2w)^12.
any term is of type $\displaystyle x^a.y^b.z^c.w^d$
constraint a+b+c+d = 12
where each can take value for [0,12]
Can you now solve it?
Spoiler - http://www.mathhelpforum.com/math-he...ber-terms.html