A second polarizer aligned with the first passes everything the first already let through, so the intensity is unchanged. With theta = 0 the cos^2 factor is one and the ledger holds steady. This is the ideal lossless case; real polarizers always absorb some fraction even when aligned, so the measured intensity drops slightly with each element.
An aligned second polarizer keeps intensity unchanged in the checked model. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
An aligned second polarizer does not reduce intensity
A second polarizer on the same axis has projection factor 1 and keeps the same value.