use substitution to solve systems of equation?

Question

y=2x
x+3y=-14

Answer 1

Use the first eq'n's expression for y in the second eq'n:
x+ 3(2x) = -14, or 7x = -14, so x = -2.
Then y = 2*-2 = -4

Answer 2

The basic method is to solve one equation for x or y and plug what it's equal to into the other equation. The example you give is a simple one, because the first equation is already solved for y. So we put it's value (2x) into the second equation, which makes it an equation with a single variable x:

x + 3(2x) = -14
x + 6x = -14
7x = -14
x = -2

Now that we know what x is, you can put it's value into either equation and solve for y. Pick the one that's easiest, in this case, the first one:

y = 2(-2)
y = -4

If we had chosen the second equation, it would look like this:

x + 3y = -14
(-2) + 3y = -14
3y = -12
y = -4 Same result, just a little more work to get it!

To prove these are the correct values, put them into each equation and see if they work:

y = 2x
-4 = 2(-2)
-4 = -4 This is correct!

x + 3y = -14
(-2) + 3(-4) = -14
(-2) + (-12) = -14
-14 = -14 This is also correct!

Answer 3

X+3(2X)=14
X+6X=14
7X=14
/7 /7
X=2
Y=2(2)
Y=4

Answer 4

y=2x
x+3y=-14
x+3(2x) =-14
7x =-14
x=-2 y= -4

Answer 5

y=2x ------------------------- (1)
x+3y=-14 ------------------- (2)

Substitute (1) into (2),

x + 3(2x) = 14
x + 6x = 14
7x = 14
x = 2

Substitute x = 2 into (1),

y = 2(2)
= 4

Hence, x = 2, y = 4

Answer 6

y=2x
x+3y=-14

x+3(2x)=-14
x+6x=-14
7x=-14
x=-2

y=2(-2)=-4
y=-4

Answer 7

x+3(2x)=-14
x+6x=1-4
7x=-14
x=-2
y=2(-2)
y=-4