solving the system

[isthisinuse?]

problem #1 3x + 3y = -9
3x - 3y = 21




problem #2 y = 4x + 6
y = 2x

 

[arthur ohlsten]

1)
3x+3y=-9
3x-3y=21

I will solve this by a method I like. you can do it by whatever method your instructor is teaching
3x+3y=-9
3x-3y=21 add the equations
-------------
6y=12
y=2 answer
substitute 2 for y in either equation
3x+6=-9
3x=-15
x=-5 answer
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(2
y=4x+6
y=2x subtract second eq. from 1st
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0=2x+6
2x=-6
x=-3 answer
y=-6

you do it by multiplying the second equation by -2 and then adding the equations. The method used is to make a term in each equation to have the same magnitude , and then adding or subtracting the equations
Arthur

 

[mmm4444bot]

I will solve this by a method I like. you can do it by whatever method your instructor is teaching
3x+3y=-9
3x-3y=21 add the equations
-------------
6y=12 Arthur meant to type 6x = 12.
y=2 answer x = 2

x=-5 answer y = -5