In Algebra 1 we're working on solving linear systems, to problems like "x=y+3 2x-y+5" And I don't even know where to start.

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Tom D. | Very patient Math Expert who likes to teachVery patient Math Expert who likes to te...

You'll learn better techniques for higher order systems, but the 2nd order system (2 eqtns with 2 unknowns) is straightforward to solve by hand. Here are the general steps

1) Place both equations in the form aX + bY = c

2) Inspect the constants of both equations to find a GCM for either X or Y

3) Multiply Either equation (or both) to achieve the GCM in both eqtns for that X or Y

4) Add or subtract the equations to get RID of that X or Y

5) Solve for that remaining Y or X

6) Substitute that first answer (YorX) to compute the other (XorY)

Let's do your example

1)

x-y=3

2x-y=5

2)Looking at the above, you'll note that if we subtract the 1st equation from the 2nd, we can make the Y-variable disappear. To be clear, I'll rewrite them

2x-y=5

-( x-y)=3

x = (5-3)=2

6) Now just pick an equation to substitute back to find y (doesn't matter which one you use)

-y=3-x (moved x to the right on 1st eqtn)

y=x-3 (multiplied by -1 on both sides)

y=(2)-3= -1 (substituted 2 into x from above)-----> (x,y)=(2,-1)

6) Lets check the other eqtn just to verify

-y =-2x + 5

y= 2x - 5 (multiplied by -1 on both sides)

y=2(2)-5= -1 (substituted 2 into x from above)-----> (x,y)=(2,-1) VERIFIED!

Instead of adding equations you could also just use substitution since we know x=y+3. Plug in x in the 2nd equation and we get

2(y+3)-y=5 Solve for y.

2y+6-y=5

y+6=5

y=-1

Now plug in y in the 1st equation and we get

x=(-1)+3=2

Hope this helps!

Parviz F. | Mathematics professor at Community CollegesMathematics professor at Community Colle...

X = y +3

2X - y = 5

X - y = 3 (1)

2X - y = 5 ( 2) / first make equations in the standard form of

/ aX + b =c

You see here that if you subtract equation equ (1) from (2)

X = 5-3 = 2

Substitute X =2 back to equation (1)

2 - y = 3 Y = 2 - 3 = -1

would I be able to talk live about this, if so you'll need a lot of patience, it will take a bit for me to understand it

There's a small error: the standard form is actually ax + by = c. You just forgot the 'y'.

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