document.write( "Question 1153034: Find the equation of the tangent to the curve x^2y-x=y^3-8 at x=0. \n" ); document.write( "
Algebra.Com's Answer #775193 by Edwin McCravy(20060)\"\" \"About 
You can put this solution on YOUR website!
x^2y-x=y^3-8 at x=0
\n" ); document.write( "
\r\n" );
document.write( "Substituting x=0,\r\n" );
document.write( "\"x%5E2y-x=y%5E3-8\"\r\n" );
document.write( "\"0%5E2y-0=y%5E3-8\"\r\n" );
document.write( "\"0=y%5E3-8\"\r\n" );
document.write( "\"8=y%5E3\"\r\n" );
document.write( "\"2=y\"\r\n" );
document.write( "\r\n" );
document.write( "So the point of tangency is (0,2), and we want the equation of the\r\n" );
document.write( "green line below:\r\n" );
document.write( "\r\n" );
document.write( "\r\n" );
document.write( "\r\n" );
document.write( "We find the slope of the tangent line, which is the\r\n" );
document.write( "same as the derivative at that point:  So we find\r\n" );
document.write( "the derivative implicitly, i.e., without solving for\r\n" );
document.write( "the independent variable y:\r\n" );
document.write( "\r\n" );
document.write( "\"x%5E2y-x=y%5E3-8\"\r\n" );
document.write( "\"x%5E2%2Aexpr%28dx%2Fdy%29%2B2xy-1=3%2Ay%5E2%2Aexpr%28dy%2Fdx%29\"\r\n" );
document.write( "\r\n" );
document.write( "We substitute x=0 and y=2 and solve for \"%22dy%22%2F%22dx%22\"\r\n" );
document.write( "\r\n" );
document.write( "\"0%5E2%2Aexpr%28dx%2Fdy%29-2%280%29%282%29-1=3%2A2%5E2%2Aexpr%28dy%2Fdx%29\"\r\n" );
document.write( "\r\n" );
document.write( "\"0-0-1=3%2A4%2Aexpr%28dy%2Fdx%29\"\r\n" );
document.write( "\r\n" );
document.write( "\"-1=12%2Aexpr%28dy%2Fdx%29\"\r\n" );
document.write( "\r\n" );
document.write( "\"-1%2F12=expr%28dy%2Fdx%29\"\r\n" );
document.write( "\r\n" );
document.write( "That's the slope of the tangent line at (0,2), which is\r\n" );
document.write( "the green line. So\r\n" );
document.write( "\r\n" );
document.write( "\"m=-1%2F12\"\r\n" );
document.write( "\r\n" );
document.write( "Since the point of tangency is the y-intercept (0,2), we can just\r\n" );
document.write( "use:\r\n" );
document.write( "\r\n" );
document.write( "\"y=mx%2Bb\"\r\n" );
document.write( "\r\n" );
document.write( "with \r\n" );
document.write( "\"matrix%281%2C3%2Cm=-1%2F12%2C%22%22%2C+b=2%29\"\r\n" );
document.write( "\r\n" );
document.write( "\"y=expr%28-1%2F12%29x%2B2\"\r\n" );
document.write( "\r\n" );
document.write( "Edwin
\n" ); document.write( "
\n" );