Question

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For the following system, if you isolated y in the first equation to use the Substitution Method, what expression would you substitute into the second equation?

4x − y = 8
2x + 3y = 9

8 − 4x

8 + 4x

−8 + 4x

−8 − 4x

Answer 1

help please

Answer 2

4x-y=8

Add y both sides wht do u gt ?

Answer 3

i dont understand

Answer 4

Adding y both sides

4x-y+y=8+y
4x=8+y

Answer 5

Gt it till right here ?

Answer 6

oh yes

Answer 7

what do i do next

Answer 8

Actually what you are being asked to do is find an expression for y in terms of x, and substitute that into the second equation.

So if your two equations are
4x − y = 8
2x + 3y = 9

Then from the first equation we have that
-y = 8 - 4x
hence
y = -8 + 4x
or
y= 4x - 8

This is the expression you would substitute into the second equation, as in
2x + 3y = 9
thus
2x + 3(4x - 8) = 9

Note the the question is NOT asking you to solve the equations. It is just asking you to find an expression for y from the first of each pair of equations which you would substitute into the second equation.

Answer 9

Oh okay

Answer 10

so it's -8-4x?

Answer 11

hello

Answer 12

No
4x - y = 8
Hence
-y = 8 - 4x
and thus
y = -(8-4x)
y = 4x - 8

Answer 13

but what if that isnt one of the choices

Answer 14

But it IS one of the choices.

Answer 15

4x - 8 is equal to exactly one of these expressions:

8 − 4x

8 + 4x

−8 + 4x

−8 − 4x

Answer 16

which one?

Answer 17

8-4x?

Answer 18

4x - 8

Can it be 8 - 4x, I don't think so, because if it were then

4x - 8 = 8 - 4x = -(4x - 8)

Answer 19

Remember that a + b = b + a. This is called the commutative property of addition.

Hence

4x - 8 = -8 + 4x