Question

Factor each trinomial by grouping. 4x^2 - 8x -21 please show work I don't get it!

Answer 1

There is no easy and straight forward way to do this, but just try breaking it down:
-if you have negative 21, you know you need to simplify it so that it is in the form (x+ )(x- )
- from here figure out what are factors of 21 (3 and 7)
-and what are factors of 4 (2)
-then mix these numbers around in the form above until they equal the trinomial

Answer 2

But I thought you had to multiply -21 and 4 which equals -84 and then I thought you had to find 2 numbers that multipy to equal =84 and add up to -8

Answer 3

oh well, that may be the case, but i have never learned it that way. and thats not exactly what i come up with for the final numbers.

Answer 4

try starting with (2x- ) (2x+ ) and put in factors of 21

Answer 5

lets do the slide and divide method
one of my favorite