This Wikipedia article of Infinite Descent says:
We have $ 3 \mid a_1^2+b_1^2 \,$. This is only true if both $a_1$ and $b_1$ are divisible by $3$.
But how can this be proved?
This Wikipedia article of Infinite Descent says:
We have $ 3 \mid a_1^2+b_1^2 \,$. This is only true if both $a_1$ and $b_1$ are divisible by $3$.
But how can this be proved?