Solve by addition method/linear equations

D

dazed&confusedonalgeb

New member
Joined
Mar 4, 2006
Messages
6
Oh, i need some help pleeeeeeeeeeeeeeeese....

solve using additon method...

3x - 2.5y = 7.125
2.5x - 3y = 7.3123

I dont even know how to start this one with decimals.. can someone help me solve this one.
 
dazed&confusedonalgeb said:
Oh, i need some help pleeeeeeeeeeeeeeeese....
solve using additon method...
3x - 2.5y = 7.125
2.5x - 3y = 7.3123
I dont even know how to start this one with decimals.. can someone help me solve this one.
Click to expand...
Multiply each term by 10000:

30000x - 25000y = 71250
25000x - 30000y = 73123

Now you can't use "decimals" as an excuse :wink:
 
dazed&confusedonalgeb said:
Oh, i need some help pleeeeeeeeeeeeeeeese....

solve using additon method...

3x - 2.5y = 7.125
2.5x - 3y = 7.3123

I dont even know how to start this one with decimals.. can someone help me solve this one.
Click to expand...
The idea is to rewrite things a little so that adding the equations will get rid of something. It takes a clue about Common Multiple to pull this off.

We have coefficients of 3 and 2.5. If all else fails, we can simple multiply by each other and get a common multiple.

Multiplying the first by 2.5

7.5x - 6.25y = 17.8125

Multiplying the second by 3

7.5x - 9y = 21.9369

See how the coefficient on 'x' is now the same? That is good. Multiply one of the equations by -1, just so they have opposite signs. Then we can just add. Subtraction is more confusing.

7.5x - 6.25y = 17.8125
-7.5x + 9y = -21.9369

Adding

2.75y = 4.1244

This is easily solved for 'y'.

You tell me what's next.
 
Have you tried division?

If you cannot solve that last equation on your own, you are absolutely NOT ready for systems of equations.
 
You must log in or register to reply here.
Top