Question 701268
Plot quantity demanded on the vertical axis
and unit price on the horizontal axis.
Let {{{ Q }}} = quantity demanded
Let {{{ p }}} = unit price
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I can write a general point-slope formula:
{{{ ( Q - 200 ) / ( p - 90 ) = ( 1200 - 200 ) / ( 40 - 90 ) }}}
{{{ ( Q - 200 ) / ( p - 90 ) = 1000 / (-50 ) }}}
{{{ ( Q - 200 ) / ( p - 90 ) = -20 }}}
{{{ Q - 200 = -20*( p - 90 ) }}}
{{{ Q = -20p + 1800 + 200 }}}
{{{ Q = -20p + 2000 }}}
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check answer:
Does it go through ( 90, 200 ) ?
{{{ Q = -20p + 2000 }}}
{{{ 200 = -20*90 + 2000 }}}
{{{ 200 = -1800 + 2000 }}}
{{{ 200 = 200 }}}
OK
Does it go through ( 40, 1200 ) ?
{{{ Q = -20p + 2000 }}}
{{{ 1200 = -20*40 + 2000 }}}
{{{ 1200 - -800 + 2000 }}}
{{{ 1200 = 1200 }}}
OK
Here's the plot:
{{{ graph( 400, 400, -20, 120, -100, 2500, -20x + 2000 ) }}}