(2x+3) (3x^2 +2x-5) Need help on Multiplying Polynomials.

Question

Thanks!

 

Answer 1

Sometimes it helps to make a grid:

 

put the "2x" and the "+3" down the side, and the   "3x^2" , the "+2x", and the "-5" across the top:

 

 

 

      3x²          +2x        -5

2x    #            #            #

+3   #             #            #

 

Then you just need to multiply as if this was a multiplication table, filling in all the "#"s

 

        3x²     +2x      -5
2x     6x³      4x²     -10x
+3    9x²       6x      -15

 

 

now just group all the like terms together and combine/simplify:

 

6x³+ (4x²+9x²) + (6x-10x) - 15

6x³ + 13x² -4x - 15