Question

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

−x + 2y = 9
4x + 5y = 9

−9 + 2y

−9 − 2y

9 − 2y

9 + 2y

Answer 1

if you solved

−x + 2y = 9

for x, what would you get?

Answer 2

i dont know

Answer 3

I'll start you off

−x + 2y = 9

−x + 2y - 2y = 9 - 2y ... Subtract 2y from both sides.

-x = 9 - 2y

and I'll let you finish up

Answer 4

you need to completely isolate x

Answer 5

9-2y

Answer 6

that's -x

NOT x itself

Answer 7

so how do you get rid of the -x and make x itself

Answer 8

just multiply everything by -1

Answer 9

what do you get when you do this?

Answer 10

-9+ 2y

Answer 11

you got it

Answer 12

so x = -9 + 2y

Answer 13

thank you :]

Answer 14

which means that you would substitute that into the second equation

Answer 15

would you mind helping me with this next one ?

Answer 16

sure i can help

Answer 17

Part 1: Decide whether you would use the graphing, substitution, or elimination method to solve the following system of equations. Explain, in complete sentences, why you chose that method.
Part 2: Solve the following system of equations and show all of your work.

4x + 3y = -1
3x + y = 3

Answer 18

substitution would be easiest, so let's use that

Answer 19

Solve equation 2 for y

3x + y = 3

3x + y - 3x = 3 - 3x

y = 3 - 3x

---------------------------

4x + 3y = -1

4x + 3(3 - 3x) = -1 ... plug in y = 3 - 3x

4x + 9 - 9x = -1

keep going to solve for x

Answer 20

what do you get