Question

When using the substitution method, what expression for x in the second equation would be substituted in the first equation?

4x – 7y = –9
x + 3y = 12

–3y + 12

3y – 12

–3y – 12

3y + 12

Answer 1

solve for x in the second equation ...

Answer 2

i think in chapter 3 or 4 they call it, "make x the subject"

Answer 3

but how will that get me an operation?

Answer 4

-3y+12. to get x alone on one side of the second eqn., subtract 3y from each side to get -3y+12=x.

Answer 5

by substituting a "value" for x into the first equation that is modeled after the second equation, we keep the overall value of the system the same; but the substitution from the second into the first will eliminate the x variable and leave us with only y variables to solve.

Answer 6

4x – 7y = –9
x + 3y = 12 --> x = 12-3y


4x – 7y = –9

4(12-3y) – 7y = –9

48 -12y – 7y = –9

48 -19y = –9

etc ....