Three Equations and Three Unknowns

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In Solving Algebraic Systems we frequently
MULTIPLY an EQUATION by a NUMBER
that will create OPPOSITE COEFFICIENTS.
Be VERY CAREFUL to MULTIPLY
both sides of the EQUATION by the number.
As can be seen in the first example below,
we MULTIPLY equation #1 by (-3)
so that the VARIABLE   "P"    will cancel.
Notice that we MULTIPLY ALL TERMS BY (-3)
5M(-3) is -15M ....   3N(-3) is -9N ...  1P(-3) is -3P ...and...4(-3) is -1

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