If $P(at^{2}, 2at)$,$Q(\frac{a}{t^{2}}, \frac{-2a}{t})$ and $S(a, 0)$ are three points,show that $\frac{1}{SP} + \frac{1}{SQ}$ is independent of $t$.

(N/A) The distance formula between two points $(x_1, y_1)$ and $(x_2, y_2)$ is $\sqrt{(x_2-x_1)^2 + (y_2-y_1)^2}$.
First,calculate $SP$:
$SP = \sqrt{(a - at^2)^2 + (0 - 2at)^2} = \sqrt{a^2(1-t^2)^2 + 4a^2t^2} = |a|\sqrt{1 - 2t^2 + t^4 + 4t^2} = |a|\sqrt{(1+t^2)^2} = |a|(1+t^2)$.
Next,calculate $SQ$:
$SQ = \sqrt{(a - \frac{a}{t^2})^2 + (0 - (-\frac{2a}{t}))^2} = \sqrt{a^2(1 - \frac{1}{t^2})^2 + \frac{4a^2}{t^2}} = |a|\sqrt{1 - \frac{2}{t^2} + \frac{1}{t^4} + \frac{4}{t^2}} = |a|\sqrt{1 + \frac{2}{t^2} + \frac{1}{t^4}} = |a|\sqrt{(1 + \frac{1}{t^2})^2} = |a|(1 + \frac{1}{t^2}) = |a|(\frac{t^2+1}{t^2})$.
Now,evaluate $\frac{1}{SP} + \frac{1}{SQ}$:
$\frac{1}{SP} + \frac{1}{SQ} = \frac{1}{|a|(1+t^2)} + \frac{1}{|a|(\frac{t^2+1}{t^2})} = \frac{1}{|a|(1+t^2)} + \frac{t^2}{|a|(1+t^2)} = \frac{1+t^2}{|a|(1+t^2)} = \frac{1}{|a|}$.
Since the result $\frac{1}{|a|}$ does not contain $t$,the expression $\frac{1}{SP} + \frac{1}{SQ}$ is independent of $t$.