compute lim_n(\frac{1}{n}+\frac{1}{2n}+\frac{1}{3n}+\cdots)?
x^2-16
4m^2+n^2+4mn
y^2+8y+15
x^2-7x+10
a^4+4a^2+4
12y=108
x^2+5x+6
4y^3-8y^2
x^2+8x+16