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? asked in Science & MathematicsMathematics · 1 decade ago

Solving systems using substitution?

I need the answer to this by using substitution:

y= 3x+2

y= 4x+8

Also, it would be nice if you explain how you got the answer too.

Update:

Wait, the first one should have a - (minus) sign not a + sign.

3 Answers

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  • 1 decade ago
    Favorite Answer

    if both equations = y, therefore

    3x+2 = 4x+8

    3x-4x = 8-2

    -x = 6

    therefore

    x = -6

    Source(s): math teacher
  • 1 decade ago

    they equal each other, because they both equal y. therefore it'll be .. :

    3x+2=4x+8 now, solve for x by canceling out the two from the left side to the ride of the = sign.

    3x+2-2=4x+8-2 so now its ...

    3x=4x+6 because you canceled out the left side already , now cancel out the x's on the right ..

    3x-4x = 4x-4x-6 so now its ...

    -1x (or just -x) = -6

    divide -1 from each side to get x=6

    sorry if i did a really bad job explaining.

    Source(s): i'm learning this now . :D
  • 1 decade ago

    This one isn't as difficult since both equations are solved for "y." Since both of them are solved for y, you can take them and set them equal to each other.

    In this case, I will substitute the second equation in for y in the first to get

    4x+8 = 3x+2

    Then, solve the equation for x to find your x-value.

    4x - 3x + 8 = 3x - 3x +2 (Subtract 3x on both sides)

    x + 8 = 2 (Simplify)

    x + 8 - 8 = 2 - 8 (Subtract 8 on both sides)

    x = -6

    Since we found that x = -6, then we can take that value and plug it in to find the y-value. You can plug-in x into either equation. Let's plug it in to the first equation.

    y = 3(-6) + 2

    y = -18 + 2

    y = -16

    Since our x-value is -6 and our y-value is -16, the point of intersection of these two lines is (-6,-16).

    Hope this helps!

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