Help with Discrete Math Homework!

5. (a) (3 points) Let f(n)=7n4+10n2, Prove That f(n)(n4) (b) (3 points) Let p be a positive Z, show that 1p+2p+..+np is O(np+1). Note: Use the C,k definition found in the book for a) and b). ANS: 6. (4 points) Find big O, and big estimates for x7y3+x5y5+x3y7. [Hint: Big- O, big- , and big- notation can be extended to functions in more than one variable. For example, the statement f(x,y) is O(g(x,y)) means that there exist constants C,k1, and k2 such that f(x,y)Cg(x,y) whenever x>k1 and y>k2.] ANS