#1
Could you guys help me solve this using the Addition/Subtraction method, and show me how to do it step by step:

3.45x + 1.63y = 7.64
2.44x - 5.83y = -6.57

Your options are:
A, (1.40, 1.71)
B, (1.37, 1.79)
C, (1.32, 1.84)
D, (1.46, 1.63)

I know how to do it with the substitution method but not the addition/subtraction method as the decimals and negatives are throwing me off.

BTW: I would post this in the Science and Maths thread but people rarely reply to that and i need this soon lol (don't mean to sound rude either) but now i'm ranting.

TL;DR: solve problem above using the addition and subtraction method and show your work please

Thanks
#4
I'm pretty sure you just add and subtract like numbers. So add and subtract all the x's, y's, and whole numbers. Then set x=0 and solve for y. Then do the same thing for y=0.

Its been years since I have done this so I may be doing it wrong.
#5
Jeez why would you ever do it that way? Substitution is just fine.

Anyway you have 3.45x and 2.44x. Find 3.45/2.44 and multiply the second equation by that number. Now both your x coefficients should be the same. Then all you do is subtract the equations (i.e. if the first two equations are x1+y1=a and x2+y2=b, then your new one is (x1-x2)+(y1-y2)=a-b, but since x1=x2, you just have y).

Am I being clear enough?

EDIT: But typically you would only do this if either the x or y term in each equation shared coefficients, then you wouldn't have to do any multiplying or dividing.
Last edited by Timothym at Jul 31, 2009,
#6
Math is for chumps. That what I told my math teacher in 11th grade before dropping her class...Then my mom made me take it as a senior :/
Quote by jrcsgtpeppers

If women can be annoyed there arent any women incongress I should be allowed to be pissed off there are no members of pink floyd or the beatles in congress.
#7
Wouldn't you just add the two equations together and solve with substitution?


Edit: Like this:


3.45x + 1.63y = 7.64
+ 2.44x - 5.83y = -6.57
5.89x - 4.20y = 1.07

And then solve using substitution?
Last edited by hamett91 at Aug 2, 2009,
#8
There's a homework help thread for this. Ah, nvme, just saw your disclaimer.
A simple way to get it in a fix is just to plug the numbers in and see which two make both equations true. Otherwise, just listen to Timothym
#9
Quote by Timothym
Jeez why would you ever do it that way? Substitution is just fine.

Anyway you have 3.45x and 2.44x. Find 3.45/2.44 and multiply the second equation by that number. Now both your x coefficients should be the same. Then all you do is subtract the equations (i.e. if the first two equations are x1+y1=a and x2+y2=b, then your new one is (x1-x2)+(y1-y2)=a-b, but since x1=x2, you just have y).

Am I being clear enough?

EDIT: But typically you would only do this if either the x or y term in each equation shared coefficients, then you wouldn't have to do any multiplying or dividing.

yeah i mentioned in my post that i knew how to do it using substitution (don't you love it how everything sounds rude over the internet sorry)
i don't understand your edit however