Question

[6.02] Use the Substitution Method to solve the following system of equations.
2x - 9y = 1
x - 4y = 1

(1, 5)

(-5, -1)

(5, 1)

(-5, 1)

Answer 1

do you know substitution method ? and tried this ?

Answer 2

hey jenn, how're ya doin?

so you have 2 equations, right?

Answer 3

yeah

Answer 4

2x - 9y = 1 EQN 1
x - 4y = 1 ENQ 2

and the substitution method means you rearrange one of the equations to get it in the from of 1 variable (ie x ) = number +/- other variable (ie y)

so rearranging equation 2
x - 4y = 1 ENQ 2 (so add 4y to both sides to get x by itself)
x - 4y +4y = 1 + 4y
x = 1 + 4y new EQN 2 or EQN 2a if you like

Answer 5

So whats the answer?

Answer 6

now equation 2a explains what x is
so now you can substitute that back into equation 1

2x - 9y = 1 and you know x = 1 + 4y
so
2(1 + 4y) - 9y = 1
2 + 8y - 9y = 1

can you solve for y from here...?

Answer 7

this is so confusing -.-

Answer 8

Add together the common variables

Answer 9

-y?

Answer 10

y= -1 ?

Answer 11

2 + 8y - 9y = 1 minus 2 from both sides
2 -2 + 8y - 9y = 1-2
-y = -1
so y = 1

Answer 12

i get it now, thanks!

Answer 13

cool, so u can solve for x now?

Answer 14

5

Answer 15

spot on dude!