Question 686822
Given:
{{{ f(-2) = -2 }}}
{{{ f(4) = -8 }}}
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A linear equation will have the form
{{{ f(x) = m*x + b }}}
{{{ f(-2) = m*(-2) + b }}}
(1) {{{ -2 = m*(-2) + b }}}
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{{{ f(4) = m*4 + b }}}
(2) {{{ -8 = m*4 + b }}}
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Now I have 2 equations with 
2 unknowns, so it's solvable
(1) {{{ -2 = m*(-2) + b }}}
(1) {{{ -2m + b = -2 }}}
and
(2) {{{ -8 = m*4 + b }}}
(2) {{{ 4m + b = -8 }}}
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Subtract (1) from (2)
(2) {{{ 4m + b = -8 }}}
(1) {{{ -(-2m) - b = -(-2) }}}
{{{ 6m = -6 }}}
{{{ m = -1 }}}
and
(1) {{{ -2m + b = -2 }}}
(1) {{{ -2*(-1) + b = -2 }}}
(1) {{{ 2 + b = -2 }}}
(1) {{{ b = -4 }}}
The function is:
{{{ f(x) = -x - 4 }}}
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check answer:
{{{ f(-2) = -(-2) - 4 }}}
{{{ f(-2) = -2 }}}
OK
{{{ f(4) = -4 - 4 }}}
{{{ f(4) = -8 }}}
OK