25s2+29s+9 has only complex factors.
If the quadratic formula s=(-29±√(292-4×25×9))/(2×25) is used, s will not be a real number.
This is because 292=841 and 4×25×9=900.
The discriminant 841-900=-59, and the square root of a negative number is a complex number (involving the imaginary √-1).
Factoring of this expression isn't possible using real numbers.
25s2+30s+9=(5s+3)2, so 25s2+29s+9=(5s+3)2-s=(5s+3-√s)(5s+3+√s) is a sort of "mock factoring".