Lecture 18 3. Solve each system of equations using either substitution or elimination. Some may not have a solution. If there are infinitely many solutions, write down the solution set. (a) ( left{egin{array}{l}3 x-6 y=2 \ 5 x+4 y=1end{array} ight. ) (b) ( left{egin{array}{l}frac{1}{2} x-2 y=6 \ 2 x-8 y=24end{array} ight. ) (c) ( left{egin{array}{l}-x+2 y=-2 \ 4 x-8 y=1end{array} ight. ) (d) ( left{egin{array}{l}frac{1}{x}+frac{1}{y}=8 \ frac{3}{x}-frac{5}{y}=0end{array} ight. ) [Hint for ( (mathrm{d}): ) Let ( u=1 / x ) and ( v=1 / y ). 4. Solve each system of equations using either substitution or elimination. Some may not have a solution. If there are infinitely many solutions, write down the solution set. (a) ( left{egin{array}{l}x+y-z=6 \ 3 x-2 y+z=-5 \ x+3 y-2 z=14end{array} ight. ) (b) ( left{egin{array}{l}x-y+z=0 \ x-y-5 z=6 \ 2 x-2 y+z=1end{array} ight. ) 5. A wireless store owner takes presale orders for a new smartphone and tablet. He gets 340 preorders for the smartphone and 250 preorders for the tablet. If the combined price of both items is ( $ 965 ) and the combined value of the preorders is ( $ 270,500 ), how much does each device cost?
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