John gave the following explanation for factoring the trinomial x2 - x - 2: "I need to find factors of -2. -1 and 2 multiply to -2 so my factors are (x - 1)(x + 2)."
Part 1: Are John's factors correct? If not, explain where he made his mistake.
Part 2: What could John have done to check the accuracy of his factors before submitting his Module 3 test?

Question

John gave the following explanation for factoring the trinomial x2 - x - 2: "I need to find factors of -2. -1 and 2 multiply to -2 so my factors are (x - 1)(x + 2)." 
Part 1: Are John's factors correct? If not, explain where he made his mistake.
Part 2: What could John have done to check the accuracy of his factors before submitting his Module 3 test?

skullpatrol · Answer

Any ideas?

anonymous · Answer

did he make his mistake from the (x-1)(x+2) ? cause it has to be (x-2)(x+1) ?

skullpatrol · Answer

Yes, his  answer does not check, right?

anonymous · Answer

yes ! so is that all there really is to it ?

skullpatrol · Answer

$$x^2 - x - 2 
eq (x-1)(x+2)$$

skullpatrol · Answer

"explain where he made his mistake"

anonymous · Answer

Part1: Johns factors are not right because both his factors must add up to -1 and multiply to -2 . So this is why his factors shouldn't be (x - 1)(x + 2) but instead should be (x-2)(x+1)

anonymous · Answer

Part2: To check he could've just FOILed and his answer would've been wrong because it would've been x2+x-2.

skullpatrol · Answer

Correct :)