simultaneous linear equation

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didaw

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Apr 12, 2019
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I am Just wondering if some one can help me out with a simultaneous linear equation?
equation 1: 1.20 Y + Z = 1.80
equation 2: Y - 5 Z = 8.5
so this is what i did
x equation 1 by 5
6 Y + 5 Z = 9
Take equation 2 from 1 like this
6 Y + 5 Z = 9
Y - 5 Z = 8.5
5 Y = 0.5
Divided both sides by 5
Y = 0.1
Substituted Y in the sum 2
0.1 - 5 Z = 8.5
- 0.1 from both sides
5 Z = 8.4
Divided 8.4 by 5
Z = 1.68
This is what happens when I put it in to the sum
1.20 x 0.1 + 1.68 = 1.80 i thought brilliant i solved it however when i put it in to the other side this happens
0.1 - 5 x 1.68 = - 8.3
However if i was to put -1.68 in to the sum it works
0.1 - 5 x -1.68 = 8.5
Am i doing something wrong hear or is the sum wrong?
any help will be realy appreciated
 
didaw said:
I am Just wondering if some one can help me out with a simultaneous linear equation?
equation 1: 1.20 Y + Z = 1.80
equation 2: Y - 5 Z = 8.5
so this is what i did
x equation 1 by 5
6 Y + 5 Z = 9
Take equation 2 from 1 like this
6 Y + 5 Z = 9
Y - 5 Z = 8.5
5 Y = 0.5
Click to expand...
Your problem is right here.
6Y + 5Z = 9
-(Y - 5Z = 8.5)
This becomes
5Y + 10Z = 0.5

What you can do is this:
6Y + 5Z = 9
+(Y - 5Z = 8.5)

In other words, add them and the Z falls out. Don't subtract.

-Dan
 
When you subtract two quantities and get 0, then the two quantities MUST be the same (else their difference will not be 0). Your problem is that 7y and -7y are NOT the same so when you subtract them you will not get 0.
After all x - x = 0 and x and x are exactly the same.
 
After my shrink finally convinced me I wasn't a mouse,
I asked him if the big cat in his hallway also knew I wasn't a mouse....
 
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