Question 965172
(1) {{{ x + 200y = -30 }}}
(2) {{{ 10x - 70y = 100 }}}
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(2) {{{ x - 7y = 10 }}}
Add {{{ 7y }}} to both sides
(2) {{{ x = 7y + 10 }}}
Subtract {{{ 10 }}} from both sides
(2) {{{ x - 10 = 7y }}}
Divide both sides by {{{ 7 }}}
(2) {{{ ( 1/7 )*x - 10/7 = y }}}
Write it the other way
(2) {{{ y = (1/7)*x - 10/7 }}}
slope = {{{ 1/7 }}}
y-intercept = {{{ -10/7 }}}
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(1) {{{ x + 200y = -30 }}}
Subtract {{{ x }}} from both sides
(1) {{{ 200y = -x - 30 }}}
Divide both sides by {{{ 200 }}}
(1) {{{ y = -( 1/200 )*x - 3/20 }}}
slope = {{{ -1/200 }}}
y-intercept = {{{ -3/20 }}} 
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(1) {{{ x + 200y = -30 }}}
(2) {{{ x - 7y = 10 }}}
Subtract (2) from (1)
(1) {{{ x + 200y = -30 }}}
(2) {{{ -x + 7y = -10 }}}
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{{{ 207y = -40 }}}
{{{ y = -40/207 }}}
Plug this result back into (2)
(2) {{{ -x + 7*( -40/207) = -10 }}}
Multiply both sides by {{{ -1 }}}
and subtract {{{ 280/207 }}} from both sides
(2) {{{ x = 10 - 280/207 }}}
(2) {{{ x = 2070/207 - 280/207 }}}
(2) {{{ x = 1790/207 }}}
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The solution seems to be:
( 1790/207 , -40/207 )
check my math