SOLUTION: For the following systems of equations in echelon form, tell how many solutions there are in nonnegative integers. x - 7y+4z = 75; 2y+7z=60. Thanks a bunch!

Algebra ->  Equations -> SOLUTION: For the following systems of equations in echelon form, tell how many solutions there are in nonnegative integers. x - 7y+4z = 75; 2y+7z=60. Thanks a bunch!       Log On


   



Question 976765: For the following systems of equations in echelon form, tell how many solutions there are in nonnegative integers. x - 7y+4z = 75; 2y+7z=60.
Thanks a bunch!

Answer by MathLover1(20849) About Me  (Show Source):
You can put this solution on YOUR website!
our matrix

%28matrix%282%2C4%2C1%2C-7%2C4%2C75%2C0%2C2%2C7%2C60%29%29

Find the pivot in the 1st column in the 1st row

%28matrix%282%2C4%2C1%2C-7%2C4%2C75%2C0%2C2%2C7%2C60%29%29

Make the pivot in the 2nd column by dividing the 2nd row by 2

%28matrix%282%2C4%2C1%2C-7%2C4%2C75%2C0%2C1%2C7%2F2%2C30%29%29

Eliminate the 2nd column

%28matrix%282%2C4%2C1%2C0%2C57%2F2%2C285%2C0%2C1%2C7%2F2%2C30%29%29

Solution set:
x+=+285+-+%2857%2F2%29z
y+=+30+-+%287%2F2%29z
z+- free
Therefore the solutions can be written as
(x, y, z) = (285+-+%2857%2F2%29z,30+-+%287%2F2%29z,z)


Because we want to find non-negative solutions, we have three inequalities
285+-+%2857%2F2%29z%3E=0
30+-+%287%2F2%29z%3E=0
z%3E=0
so,
285+%3E=%2857%2F2%29z
30+%3E=%287%2F2%29z
285%2F%2857%2F2%29+%3E=z
30%2F%287%2F2%29+%3E=z
z%3C=10+
z%3C=8.57+
and
z%3E=0
so, the integer values of z satisfying all of those inequalities z%3E=0,z%3C=8.57+, and z%3C=10+ are
z=0,1,2,3,4,5,6,7,8
so, there will be nine non-negative solutions