Question

Show how you would solve by Substitution:
2x + y = 0
x – 3y = -7


Show how you would solve by Elimination: 3x + 4y = 1
5x – 3y = 21

Answer 1

for substitution, I would, um, substitute. The 1st equation tells you that

y = -2x

So, substitute that into the 2nd equation to get

x-3(-2x) = -7
x+6x = -7
7x = -7
x = -1
Now you can find y.

As for elimination,

3x + 4y = 1
5x – 3y = 21

to eliminate y, multiply the 1st by 3 and the 2nd by 4 to get

9x+12y = 3
20x-12y = 84

now add them up and you have

29x = 87
x = 3
Now you can find y.