You need two equations to use the addition method.
Double first equation: 2x + 2y = 4 Subtract this from second equation giving 5y = 5 so y = 1 and x = 1
solve system equation using addition method 3x-y=9 2x+y=6
8.00 − 5.91 = 2.09 (Method is to first subtract 2.09 from 8.00, which equals 5.91 If you then subtract 5.91 from 8.00 the answer will be 2.09)
From first equation, -y = 3x + 3. Substitute in second equation: -3x + 5(3x + 3) = -21 ie 12x = -36 so x = -3 and y = -(-9 + 3) = 6. Easier method: subtract first equation from second giving -4y = -24 so y = 6, this in first equation gives -6 = 3x + 3, ie 3x = -9 so x = -3
The answer depends on the equation: there is no single method which can be used for all equations.
Completing the square is a method to solve quadratic equations. To use this method you take the number without a variable and subtract it from both sides, so that it is on the opposite side of the equation. Then add the square of half the coefficient of the x-term to both sides. This will give you a perfect square equation to solve for.
how do you use the substitution method for this problem 2x-3y=-2 4x+y=24