SOLUTION: Solve this system using Cramer's rule {{{system(5x-12y=4, 4x-7y=-2)}}}

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Question 176914This question is from textbook
: Solve this system using Cramer's rule
system%285x-12y=4%2C+4x-7y=-2%29
This question is from textbook

Found 2 solutions by stanbon, Edwin McCravy:
Answer by stanbon(48568) About Me  (Show Source):
You can put this solution on YOUR website!
5x-12y=4
4x-7y=-2
---------------
coefficient determinant: (5*-7) - (-12)*4 = -35 + 48 = 13
---------------------
x-coefficient determinant: (4*-7) - (-12*-2) = -28 -24 = -52
-------------------------
y-coefficient determinant: (5*-2) - (4*4) = -10-16 = -26
------------------------------
Solution: x = -52/13 = -4 ; y = -26/13 = -2
====================================================
Cheers,
Stan H.

Answer by Edwin McCravy(6938) About Me  (Show Source):
You can put this solution on YOUR website!
Edwin's solution:

system%285x-12y+=+4%2C4x-7y=-2%29

Write this:

matrix%281%2C3%2Cx%2C%27=%27%2Cabs%28matrix%282%2C2%2C__%2C__%2C__%2C__%29%29%2Fabs%28matrix%282%2C2%2C__%2C__%2C__%2C__%29%29%29 and matrix%281%2C3%2Cy%2C%27=%27%2Cabs%28matrix%282%2C2%2C__%2C__%2C__%2C__%29%29%2Fabs%28matrix%282%2C2%2C__%2C__%2C__%2C__%29%29%29

First fill in both denominators with the
coefficients as they appear left of the equal signs, like thismatrix%282%2C2%2C5%2C-12%2C4%2C-7%29

matrix%281%2C3%2Cx%2C%27=%27%2Cabs%28matrix%282%2C2%2C__%2C__%2C__%2C__%29%29%2Fabs%28matrix%282%2C2%2C5%2C-12%2C4%2C-7%29%29%29 and matrix%281%2C3%2Cy%2C%27=%27%2Cabs%28matrix%282%2C2%2C__%2C__%2C__%2C__%29%29%2Fabs%28matrix%282%2C2%2C5%2C-12%2C4%2C-7%29%29%29

Now since x appears FIRST in the problem, fill in
the FIRST column for x with the numbers on the right of the
equal sign, namely these: matrix%282%2C1%2C4%2C-2%29

matrix%281%2C3%2Cx%2C%27=%27%2Cabs%28matrix%282%2C2%2C4%2C__%2C-2%2C__%29%29%2Fabs%28matrix%282%2C2%2C5%2C-12%2C4%2C-7%29%29%29 and matrix%281%2C3%2Cy%2C%27=%27%2Cabs%28matrix%282%2C2%2C__%2C__%2C__%2C__%29%29%2Fabs%28matrix%282%2C2%2C5%2C-12%2C4%2C-7%29%29%29

Now since y appears SECOND in the problem, fill in
the SECOND column for y with the numbers on the right of the
equal sign, namely these: matrix%282%2C1%2C4%2C-2%29

matrix%281%2C3%2Cx%2C%27=%27%2Cabs%28matrix%282%2C2%2C4%2C__%2C-2%2C__%29%29%2Fabs%28matrix%282%2C2%2C5%2C-12%2C4%2C-7%29%29%29 and matrix%281%2C3%2Cy%2C%27=%27%2Cabs%28matrix%282%2C2%2C__%2C4%2C__%2C-2%29%29%2Fabs%28matrix%282%2C2%2C5%2C-12%2C4%2C-7%29%29%29

Complete the determinants by bringing the columns below up
to the top:

matrix%281%2C3%2Cx%2C%27=%27%2Cabs%28matrix%282%2C2%2C4%2C-12%2C-2%2C-7%29%29%2Fabs%28matrix%282%2C2%2C5%2C-12%2C4%2C-7%29%29%29 and matrix%281%2C3%2Cy%2C%27=%27%2Cabs%28matrix%282%2C2%2C5%2C4%2C4%2C-2%29%29%2Fabs%28matrix%282%2C2%2C5%2C-12%2C4%2C-7%29%29%29

To evaluate abs%28matrix%282%2C2%2CA%2CB%2CC%2CD%29%29, use this formula.
which amounts to subtracting the diagonal products:

 abs%28matrix%282%2C2%2CA%2CB%2CC%2CD%29%29+=+AD+-+BC 

matrix%281%2C5%2Cx%2C%27=%27%2Cabs%28matrix%282%2C2%2C4%2C-12%2C-2%2C-7%29%29%2Fabs%28matrix%282%2C2%2C5%2C-12%2C4%2C-7%29%29%2C%27=%27%2C%28%284%29%28-7%29-%28-12%29%28-2%29%29%2F%28%285%29%28-7%29-%28-12%29%284%29%29%29

matrix%281%2C13%2Cx%2C%27=%27%2Cabs%28matrix%282%2C2%2C4%2C-12%2C-2%2C-7%29%29%2Fabs%28matrix%282%2C2%2C5%2C-12%2C4%2C-7%29%29%2C%27=%27%2C%28%284%29%28-7%29-%28-12%29%28-2%29%29%2F%28%285%29%28-7%29-%28-12%29%284%29%29%2C%27=%27%2C%28%28-28%29-%2824%29%29%2F%28%28-35%29-%28-48%29%29%2C%27=%27%2C%28-52%29%2F%28-35%2B48%29%2C%27=%27%2C%28-52%29%2F13%2C+%27=%27%2C-4%29

Now for y.  We only have to do the top
determinant because we have already done
the bottom determinant, and found it to be 13, so

matrix%281%2C11%2Cy%2C%27=%27%2Cabs%28matrix%282%2C2%2C5%2C4%2C4%2C-2%29%29%2Fabs%28matrix%282%2C2%2C5%2C-12%2C4%2C-7%29%29%2C%27=%27%2C%28%285%29%28-2%29-%284%29%284%29%29%2F13%2C+%27=%27%2C+%28%28-10%29-%2816%29%29%2F13%2C+%27=%27%2C%28-26%29%2F13%2C+%27=%27%2C+-2%29

Edwin