α β 2 3 π ϕ ∞ ( α 2 + β 2 + 2 α β ) ∑ i = 0 n {\displaystyle \alpha \beta {\frac {2}{3}}\pi \phi \infty {\sqrt {(}}\alpha ^{2}+\beta ^{2}+2\alpha \beta )\sum _{i=0}^{n}}
