Which is a factor of 2n^2-5n-42a 2n-7 b 3 - 2nc 3-2n^2d 4-2n^2

Split the middle term. 

(2n²-5n)-42

Multiply the coefficient of the first term (2 is the coefficient of 2n²) by the constant (-42, it's constant because there are no variables attached). 

2 x (-42) = -84 

Find the factor of -84 that equals your middle term (-5)

The factors of 84 are as follows (remember that if either number is negative, you'll get -84):
84*1
42*2
28*3
21*4
14*6
12*7

What two numbers, when added or subtracted, equal the middle term? 12-7 = 5, but your number is a negative, so how do you do get that 5 to be negative? -12+7 = -5, but make that easier to understand 7-12 = -5, and now add your variable back to get 7n-12n = -5n

Rewrite your equation using the split middle term.

2n²+7n-12n-42

Pull out the factors and add up the first two terms.

n*(2n+7) = 2²+7n

-6(2n+7) = -12n-42

The numbers inside the parenthesis give you one half of your new equation, combine the numbers outside the parentheses to get your second half.

(n-6) (2n+7)

In regards to your answer, there are three possibilities:

1) You wrote the initial equation incorrectly
2) You wrote the answers incorrectly
3) Whoever created the question wrote the equation or the answers wrong, and the answer is not present.

Distance=slopeslope is -2/4which equals-1/2the distance between these two points is -1/2