To start to solve the system of equations below, which number would you multiply in the equation -2x-5y=-1? the two equations are -2x-5y=-1 and 4x+2y=8

  The first equation can be multiplied by 2.

Step-by-step explanation:

The x-coefficients are -2 and 4. If the first one of these is multiplied by 2, it will be the opposite of the second of these. That is 2·(-2) = -4. When -4 and 4 are added, the result is 0, so the x-variable will be eliminated.

To solve these equations by "elimination", you look for simple relationships between the coefficients that will let you combine them to get zero.

Here's the rest of the solution.

  2(-2x-5y) +(4x+2y) = 2(-1) +(8) . . . . after multiplying the first equation by 2 and adding the second equation

  -4x -10y +4x +2y = -2 +8 . . . . . the result of eliminating parentheses

  -8y = 6 . . . . . the result of collecting terms

  y = -6/8 = -3/4 . . . . divide by the y-coefficient

Since all of the coefficients in the second equation are even, a factor of 2 can be removed, and the equation written as ...

   2x +y = 4

This can be solved for x, so you have ...

  x = (4 -y)/2 = 2 -(y/2)

Filling in the above value of y, we find x to be ...

  x = 2 -(-3/4)/2

  x = 2 3/8

Comment on eliminating y instead of x

If you divide the second equation by 2 so that y has a coefficient of 1, then you can multiply this equation by 5 to give y a coefficient that is the opposite of the coefficient -5 in the first equation. Then the elimination looks like

  (-2x -5y) +5(2x +y) = (-1) +5(4)

  -2x -5y +10x +5y = -1 +20 . . . . eliminate parentheses

  8x = 19 . . . . simplify

  x = 19/8 = 2 3/8 . . . . divide by the coefficient of x