<PRE><B>Question 204756</B>
eliminate x from the 1st and 3rd equations by:
multiply the 1st equation by 5:
15x + 20y + 5z = 35
multiply the 3rd equation by 3:
-15x + 9y + 24z = -93
add them up:
15x  + 20y + 5z  = 35
-15x + 9y  + 24z = -93
------------------------- (+)
29y + 29z = -58
------------------ (divide each side by 29)
y + z = -2


subtract the 2nd equation from the problem with this new equation:
2y + z = 3
y  + z = -2
------------- (-)
y = 5


substitute the value of y into 2nd equation:
2y + z = 3
2*5 + z = 3
10+ z = 3
z = 3 - 10 = -7


substitute the value of y and z into the 1st equation:
3x + 4y + z = 7
3x + 4*5 + (-7) = 7
3x + 20 - 7 = 7
3x + 13 = 7
3x = 7 - 13
3x = -6
x = -6/3 = -2


so, x = -2, y = 5, z = -7




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