Question

Using the Elimination method Solve the system:x+y-z=143x+2y+4z=17-x+5y+z=8

Answer 1

Given the system of equations:

x + y - z = 4 eq.(1)

3x + 2y + 4z = 17 eq.(2)

-x + 5y + z = 8 eq.(3)

Add the equations 1 and 3

so,

x + y - z + ( -x + 5y + z ) = 4 + 8

x + y - z - x + 5y + z = 12

6y = 12

y = 12/6 = 2

Substitute with y at eq. (1)

So,

x + 2 - z = 4

x - z = 4 - 2

x - z = 2 eq. (4)

Substitute with y at eq.(2)

3x + 2 * 2 + 4z = 17

3x + 4 + 4z = 17

3x + 4z = 17 - 4

3x + 4z = 13 eq.(5)

solve the equations (4) and (5) together

x - z = 2

3x + 4z = 13

Multiply [ x - z = 2 ] by 4

4x - 4z = 8

3x + 4z = 13

Add the last two equations

4x - 4z + 3x + 4z = 8 + 13

7x = 21

Divide both sides by 7

x = 21/7 = 3

So, x = 3 and y = 2

Substitute with the values of x and y at the equation [ -x + 5y + z = 8 ]

So,

-3 + 5 * 2 + z = 8

solve for z

-3 + 10 + z = 8

z = 8 + 3 - 10

z = 11 - 10 = 1

So,

x = 3 , y = 2 and z = 1