Looking at we can see that the first term is and the last term is where the coefficients are 1 and 2 respectively.
Now multiply the first coefficient 1 and the last coefficient 2 to get 2. Now what two numbers multiply to 2 and add to the middle coefficient -1? Let's list all of the factors of 2:
Factors of 2:
1,2
-1,-2 ...List the negative factors as well. This will allow us to find all possible combinations
These factors pair up and multiply to 2
1*2
(-1)*(-2)
note: remember two negative numbers multiplied together make a positive number
Now which of these pairs add to -1? Lets make a table of all of the pairs of factors we multiplied and see which two numbers add to -1
First Number
Second Number
Sum
1
2
1+2=3
-1
-2
-1+(-2)=-3
None of these pairs of factors add to -1. So the expression cannot be factored