All you have to do is substitute the y value from the 1st equation into the second equation and solve...
a) y= 2-x 5x + 4y = 5
Substitute (2-x) into the second equation anywhere there is a y...
5x + 4y = 5 5x + 4(2-x) = 5
Now solve
5x + 8 - 4x = 5 5x - 4x + 8 = 5 x + 8 = 5 x = -3
Now that you have a solution for x, substitute -3 into either of the original equations anywhere there is an x then solve for y...
y = 2 - x y = 2 - (-3) y = 2+3 = 5
You solved for x and got -3 and solved for y and got 5, so your solution set is (-3, 5).
Now check it by substituting both numbers into one of the original equations and you should have a true statement if it is correct...
y = 2 - x 5 = 2 - (-3) 5 = 2+3 5 = 5
True statement... it checks!
note* during the check, if the equation would have worked out to something like 2 = 5, then that is a false statement therefore the solution set would be wrong and you'd have to go back and find the mistake.
