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Solve the following system of linear equations:

 

x+ 2y+ 3z+ 4u=20

-x + 5 y +2 u=13

x+ y+ z+ u =10

-x+y-z+u= -2

 

Solve the following system:
{4 u+x+2 y+3 z = 20 |     (equation 1)
2 u-x+5 y = 13 |     (equation 2)
u+x+y+z = 10 |     (equation 3)
u-x+y-z = -2 |     (equation 4)
Add equation 1 to equation 2:
{x+2 y+3 z+4 u = 20 |     (equation 1)
0 x+7 y+3 z+6 u = 33 |     (equation 2)
x+y+z+u = 10 |     (equation 3)
-x+y-z+u = -2 |     (equation 4)
Subtract equation 1 from equation 3:
{x+2 y+3 z+4 u = 20 |     (equation 1)
0 x+7 y+3 z+6 u = 33 |     (equation 2)
0 x-y-2 z-3 u = -10 |     (equation 3)
-x+y-z+u = -2 |     (equation 4)
Multiply equation 3 by -1:
{x+2 y+3 z+4 u = 20 |     (equation 1)
0 x+7 y+3 z+6 u = 33 |     (equation 2)
0 x+y+2 z+3 u = 10 |     (equation 3)
-x+y-z+u = -2 |     (equation 4)
Add equation 1 to equation 4:
{x+2 y+3 z+4 u = 20 |     (equation 1)
0 x+7 y+3 z+6 u = 33 |     (equation 2)
0 x+y+2 z+3 u = 10 |     (equation 3)
0 x+3 y+2 z+5 u = 18 |     (equation 4)
Subtract 1/7 × (equation 2) from equation 3:
{x+2 y+3 z+4 u = 20 |     (equation 1)
0 x+7 y+3 z+6 u = 33 |     (equation 2)
0 x+0 y+(11 z)/7+(15 u)/7 = 37/7 |     (equation 3)
0 x+3 y+2 z+5 u = 18 |     (equation 4)
Multiply equation 3 by 7:
{x+2 y+3 z+4 u = 20 |     (equation 1)
0 x+7 y+3 z+6 u = 33 |     (equation 2)
0 x+0 y+11 z+15 u = 37 |     (equation 3)
0 x+3 y+2 z+5 u = 18 |     (equation 4)
Subtract 3/7 × (equation 2) from equation 4:
{x+2 y+3 z+4 u = 20 |     (equation 1)
0 x+7 y+3 z+6 u = 33 |     (equation 2)
0 x+0 y+11 z+15 u = 37 |     (equation 3)
0 x+0 y+(5 z)/7+(17 u)/7 = 27/7 |     (equation 4)
Multiply equation 4 by 7:
{x+2 y+3 z+4 u = 20 |     (equation 1)
0 x+7 y+3 z+6 u = 33 |     (equation 2)
0 x+0 y+11 z+15 u = 37 |     (equation 3)
0 x+0 y+5 z+17 u = 27 |     (equation 4)
Subtract 5/11 × (equation 3) from equation 4:
{x+2 y+3 z+4 u = 20 |     (equation 1)
0 x+7 y+3 z+6 u = 33 |     (equation 2)
0 x+0 y+11 z+15 u = 37 |     (equation 3)
0 x+0 y+0 z+(112 u)/11 = 112/11 |     (equation 4)
Multiply equation 4 by 11/112:
{x+2 y+3 z+4 u = 20 |     (equation 1)
0 x+7 y+3 z+6 u = 33 |     (equation 2)
0 x+0 y+11 z+15 u = 37 |     (equation 3)
0 x+0 y+0 z+u = 1 |     (equation 4)
Subtract 15 × (equation 4) from equation 3:
{x+2 y+3 z+4 u = 20 |     (equation 1)
0 x+7 y+3 z+6 u = 33 |     (equation 2)
0 x+0 y+11 z+0 u = 22 |     (equation 3)
0 x+0 y+0 z+u = 1 |     (equation 4)
Divide equation 3 by 11:
{x+2 y+3 z+4 u = 20 |     (equation 1)
0 x+7 y+3 z+6 u = 33 |     (equation 2)
0 x+0 y+z+0 u = 2 |     (equation 3)
0 x+0 y+0 z+u = 1 |     (equation 4)
Subtract 3 × (equation 3) from equation 2:
{x+2 y+3 z+4 u = 20 |     (equation 1)
0 x+7 y+0 z+6 u = 27 |     (equation 2)
0 x+0 y+z+0 u = 2 |     (equation 3)
0 x+0 y+0 z+u = 1 |     (equation 4)
Subtract 6 × (equation 4) from equation 2:
{x+2 y+3 z+4 u = 20 |     (equation 1)
0 x+7 y+0 z+0 u = 21 |     (equation 2)
0 x+0 y+z+0 u = 2 |     (equation 3)
0 x+0 y+0 z+u = 1 |     (equation 4)
Divide equation 2 by 7:
{x+2 y+3 z+4 u = 20 |     (equation 1)
0 x+y+0 z+0 u = 3 |     (equation 2)
0 x+0 y+z+0 u = 2 |     (equation 3)
0 x+0 y+0 z+u = 1 |     (equation 4)
Subtract 2 × (equation 2) from equation 1:
{x+0 y+3 z+4 u = 14 |     (equation 1)
0 x+y+0 z+0 u = 3 |     (equation 2)
0 x+0 y+z+0 u = 2 |     (equation 3)
0 x+0 y+0 z+u = 1 |     (equation 4)
Subtract 3 × (equation 3) from equation 1:
{x+0 y+0 z+4 u = 8 |     (equation 1)
0 x+y+0 z+0 u = 3 |     (equation 2)
0 x+0 y+z+0 u = 2 |     (equation 3)
0 x+0 y+0 z+u = 1 |     (equation 4)
Subtract 4 × (equation 4) from equation 1:
{x+0 y+0 z+0 u = 4 |     (equation 1)
0 x+y+0 z+0 u = 3 |     (equation 2)
0 x+0 y+z+0 u = 2 |     (equation 3)
0 x+0 y+0 z+u = 1 |     (equation 4)
Collect results:
Answer: | 
| {x = 4
y = 3
z = 2
u = 1

Oct 26, 2015

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