Question 433203
(1) {{{  9x + 2y = 2 }}}
(2) {{{ 21x + 6y = 4 }}}
Multiply both sides of (1) by {{{3}}} and subtract
(2) from (1)
(1) {{{  27x + 6y = 6 }}}
(2) {{{ -21x - 6y = -4 }}}
{{{ 6x = 2 }}}
{{{ x= 1/3 }}}
and
(1) {{{  9*(1/3) + 2y = 2 }}}
{{{3 + 2y = 2 }}}
{{{ 2y = -1 }}}
{{{ y = -1/2 }}}
check answer:
(2) {{{ 21x + 6y = 4 }}}
{{{ 21*(1/3) + 6*(-1/2) = 4 }}}
{{{ 7 - 3 = 4 }}}
{{{ 4 = 4 }}}
OK
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(1) {{{2x + 3y = 18}}}
(2) {{{5x – y = 11}}}
Multiply both sides of (2) by {{{3}}},
The add the equations
(1) {{{2x + 3y = 18}}}
(2) {{{15x – 3y = 33}}}
{{{ 17x = 51 }}}
{{{ x = 3 }}}
and
(1) {{{2*3 + 3y = 18}}}
{{{ 6 + 3y = 18 }}}
{{{ 3y = 12 }}}
{{{ y = 4 }}}
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