Find the common factor in the quadratic polynomials x² + 8x + 15 and x² + 3x – 10.

Given Polynomial : x² + 8x + 15 

                                = x² + 5x + 3x + 15  

                                = (x + 3) (x + 5)
 

Given polynomial : x² + 3x – 10 

                             = x² + 5x – 2x – 10 

                             = (x – 2) (x + 5)
Clearly, the common factor is x + 5.