document.write( "Question 1080724: please help!!!\r
\n" ); document.write( "\n" ); document.write( "Find the equation for the tangent lines, and the normal lines, to the hyperbolas y^2/4-x^2/2=1 when x=4.
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Algebra.Com's Answer #694829 by Fombitz(32388)\"\" \"About 
You can put this solution on YOUR website!
The slope of the tangent line is equal to the value of the derivative at that point.
\n" ); document.write( "\"y%5E2%2F4-x%5E2%2F2=1\"
\n" ); document.write( "\"y%5E2-2x%5E2=4\"
\n" ); document.write( "Implicitly differentiate,
\n" ); document.write( "\"2ydy-4xdx=0\"
\n" ); document.write( "\"2ydy=4xdx\"
\n" ); document.write( "\"dy%2Fdx=2%28x%2Fy%29\"
\n" ); document.write( "So then,
\n" ); document.write( "\"y%5E2-2%284%29%5E2=4\"
\n" ); document.write( "\"y%5E2-32=4\"
\n" ); document.write( "\"y%5E2=36\"
\n" ); document.write( "\"y=6\" and \"y=-6\"
\n" ); document.write( "So for (4,6),
\n" ); document.write( "\"m=dy%2Fdx=2%284%2F6%29=4%2F3\"
\n" ); document.write( "Using the point slope form of a line,
\n" ); document.write( "\"y-6=%284%2F3%29%28x-4%29\"
\n" ); document.write( "\"y-6=%284%2F3%29x-16%2F3%7D%7D%0D%0A%7B%7B%7By=%284%2F3%29x-16%2F3%2B18%2F3\"
\n" ); document.write( "\"y=%284%2F3%29x%2B2%2F3\"
\n" ); document.write( "and for (4,-6)
\n" ); document.write( "\"m=-4%2F3\"
\n" ); document.write( "and
\n" ); document.write( "\"y%2B6=-%284%2F3%29%28x-4%29\"
\n" ); document.write( "\"y%2B6=-%284%2F3%29x%2B16%2F3%29\"
\n" ); document.write( "\"y=-%284%2F3%29x%2B16%2F3-18%2F3%29\"
\n" ); document.write( "\"y=-%284%2F3%29x-2%2F3\"
\n" ); document.write( "To get the normal lines, you know that the tangent and normal lines are perpendicular to each other.
\n" ); document.write( "So the slopes are negative reciprocals,
\n" ); document.write( "\"m%5B1%5D%2A%284%2F3%29=-1\"
\n" ); document.write( "\"m%5B1%5D=-3%2F4\"
\n" ); document.write( "and
\n" ); document.write( "\"m%5B2%5D%2A%28-4%2F3%29=-1\"
\n" ); document.write( "\"m%5B2%5D=3%2F4\"
\n" ); document.write( "So then,
\n" ); document.write( "(4,6)
\n" ); document.write( "\"y-6=%283%2F4%29%28x-4%29\"
\n" ); document.write( "(4,-6)
\n" ); document.write( "\"y%2B6=%283%2F4%29%28x-4%29\"
\n" ); document.write( "I leave those to you to put into slope-intercept form.\r
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