Official solution
RHS = \[\sum\limits_{r = 0}^{99} {(100 - r)(100 + r)} \]
\[ = {(100)^3} - {{99 \times 100 \times 199} \over 6} = {(100)^3} - (1650)199\]
LHS = (100) (\alpha\] - (199) (\beta\]
So, \[\alpha\] = 3, \[\beta\] = 1650
Slope = tan\[\theta\] = \[{\beta \over \alpha }\]
\[ \Rightarrow \] tan\[\theta\] = 550