Question 351021
a) Add the equations,
{{{x+y+x-y=7+9}}}
{{{2x=16}}}
{{{highlight( x=8)}}}
Then from the first equation,
{{{8+y=7}}}
{{{highlight(y=-1)}}}
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b)Add the equations,
{{{x - 2y -x + 5y = -1+4}}}
{{{3y=3}}}
{{{highlight(y=1)}}}
Then from the first equation,
{{{x-2=-1}}}
{{{highlight( x=1)}}}
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c) 
1.{{{3x + 5y = -11}}}
2.{{{x - 2y = 11 }}}
 Multiply eq. 2 by (-3) and add the equations together,
{{{3x+5y-3x+6y=-11-33}}}
{{{11y=-44}}}
{{{highlight(y=-4)}}}
Then from eq. 2,
{{{x+8=11}}}
{{{highlight(x=3)}}}
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d) Rearrange the first equation, then subtract the first from the second,
{{{2x = 2-y}}}
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{{{2x+y=2}}}
{{{3x + y = -1 }}}
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{{{3x+y-2x-y=-1-2}}}
{{{highlight(x=-3)}}}
Then from the first equation,
{{{-6+y=2}}}
{{{highlight(y=8)}}}