Simultaneous Equation 2 unknowns - help

meano

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Oct 27, 2014
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Apologies if I haven't set this out correctly.

Equation is V = U + AT

For EQ 1, V=21, T=3.5

For EQ 2, V=33, T=6.1


Equation 1
(1) U + 3.5A = 21
(2) U = 21 - 3.5A
(3) U = 21 - (3.5 * 5.625)
(4) U = 21 - 19.6875
(5) U = 1.3125
Equation 2
(1) U + 6.1A = 33
(2) 21 - 3.5A + 6.1A = 33
(3) 21 - 9.6A = 33
(4) 9.6A = 54
(5) A = 54/9.6 = 5.625
Verify
1.3125 + (3.5 * 5.625) = 21
1.3125 + 19.6875 = 21
Verify
1.3125 + (6.1 * 5.625)
1.3125 + 34.3125 = 35.625


As you can see, equation 2 does not work out, however it will be correct if you do 34.3125 - 1.3125 = 33. I obviously need to do the subtraction but can't see where I need to change the positive to a negative.

I appreciate the help.

Thanks
 
Apologies if I haven't set this out correctly.

Equation is V = U + AT

For EQ 1, V=21, T=3.5

For EQ 2, V=33, T=6.1


Equation 1
(1) U + 3.5A = 21
(2) U = 21 - 3.5A
(3) U = 21 - (3.5 * 5.625)
(4) U = 21 - 19.6875
(5) U = 1.3125
Equation 2
(1) U + 6.1A = 33
(2) 21 - 3.5A + 6.1A = 33..... Incorrect
How did you get That?
(3) 21 - 9.6A = 33
(4) 9.6A = 54
(5) A = 54/9.6 = 5.625
Verify
1.3125 + (3.5 * 5.625) = 21
1.3125 + 19.6875 = 21
Verify
1.3125 + (6.1 * 5.625)
1.3125 + 34.3125 = 35.625


As you can see, equation 2 does not work out, however it will be correct if you do 34.3125 - 1.3125 = 33. I obviously need to do the subtraction but can't see where I need to change the positive to a negative.

I appreciate the help.

Thanks
.
 
Step 2 of equation 1 gives U. Enabling you to work out A in equation 2.
 
Apologies if I haven't set this out correctly.

Equation is V = U + AT

For EQ 1, V=21, T=3.5

For EQ 2, V=33, T=6.1


Equation 1
(1) U + 3.5A = 21
(2) U = 21 - 3.5A
(3) U = 21 - (3.5 * 5.625)
(4) U = 21 - 19.6875
(5) U = 1.3125
Equation 2
(1) U + 6.1A = 33
(2) 21 - 3.5A + 6.1A = 33
(3) 21 - 9.6A = 33
(4) 9.6A = 54
(5) A = 54/9.6 = 5.625
Verify
1.3125 + (3.5 * 5.625) = 21
1.3125 + 19.6875 = 21
Verify
1.3125 + (6.1 * 5.625)
1.3125 + 34.3125 = 35.625


As you can see, equation 2 does not work out, however it will be correct if you do 34.3125 - 1.3125 = 33. I obviously need to do the subtraction but can't see where I need to change the positive to a negative.

I appreciate the help.

Thanks

Okay now I understand the problem!!

21 = U + 3.5*A...............(1)
33 = U + 6.1*A...............(2) 2 equations 2 unknowns (U and A)

subtract (1) from (2)

33 - 21 = U - U + A*(6.1 - 3.5)

12 = 2.6 * A → A = 12/2.6 → A = 4.615385

Using (1)

21 = U + 3.5*4.615385 → U = 4.846154

Now check the answers......
 
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