document.write( "Question 1009294: The gas mileage for a certain vehicle can be approximated by m = −0.04x2 + 3.6x − 49, where x is the speed of the vehicle in mph. Determine the speed(s) at which the car gets 30 mpg. Round to the nearest mph. \n" ); document.write( "

Algebra.Com's Answer #624848 by josmiceli(19441) $\"\"$ $\"About$

You can put this solution on YOUR website!
$\"+m+=+-.04x%5E2+%2B+3.6x+-+49+\"$
\n" ); document.write( " $\"+30+=+-.04x%5E2+%2B+3.6x+-+49+\"$
\n" ); document.write( " $\"+-.04x%5E2+%2B+3.6x+-+79+=+0+\"$
\n" ); document.write( " $\"+-4x%5E2+%2B+360x+-+7900+=+0+\"$
\n" ); document.write( " $\"+-x%5E2+%2B+90x+-+1975+=+0+\"$
\n" ); document.write( "Use quadratic formula
\n" ); document.write( " $\"+x+=+%28+-90+%2B-+sqrt%28+90%5E2-4%2A%28-1%29%2A%28-1975%29+%29%29%2F%282%2A%28-1%29%29+\"$
\n" ); document.write( " $\"+x+=+%28+-90+%2B-+sqrt%28+8100+-+7900+%29%29%2F%28-2%29+\"$
\n" ); document.write( " $\"+x+=+%28+-90+%2B-+sqrt%28+200+%29%29%2F%28-2%29+\"$
\n" ); document.write( " $\"+x+=+%28+-90+%2B+14.142+%29%2F%28-2%29+\"$
\n" ); document.write( " $\"+x+=+37.93+\"$
\n" ); document.write( "38 mi/hr
\n" ); document.write( "------------
\n" ); document.write( "and, also:
\n" ); document.write( " $\"+x+=+%28+-90+-+14.142+%29%2F%28-2%29+\"$
\n" ); document.write( " $\"+x+=+%28+-+104.142+%29+%2F+%28+-2+%29+\"$
\n" ); document.write( " $\"+x+=+52.07+\"$
\n" ); document.write( "52 mi/hr
\n" ); document.write( "--------------
\n" ); document.write( "check:
\n" ); document.write( " $\"+30+=+-.04x%5E2+%2B+3.6x+-+49+\"$
\n" ); document.write( " $\"+30+=+-.04%2A38%5E2+%2B+3.6%2A38+-+49+\"$
\n" ); document.write( " $\"+30+=+-.04%2A1444+%2B+136.8+-+49+\"$
\n" ); document.write( " $\"+30+=+-57.76+%2B+136.8+-+49+\"$
\n" ); document.write( " $\"+30+=+30.04+\"$
\n" ); document.write( "close enough
\n" ); document.write( "You can check the other solution \n" ); document.write( "

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