Solve each system using elimination. $$ \left\{\begin{array}{l} r+s-3 t=21 \\ r+4 s=9 \\ 5 s+t=-4 \end{array}\right. $$
Added by Mark B.
Step 1
This gives us: $$ \begin{aligned} (r+s-3t)-(r+4s)&=21-9 \\ -s-3t&=12 \\ \end{aligned} $$ Show more…
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