document.write( "Question 79984: A line passing through (5,-8) and (9,y) is perpendicular to a line with slope -4/9. Find the value of y. \n" ); document.write( "
Algebra.Com's Answer #57356 by ankor@dixie-net.com(22740)\"\" \"About 
You can put this solution on YOUR website!
A line passing through (5,-8) and (9,y) is perpendicular to a line with slope -4/9. Find the value of y.
\n" ); document.write( ":
\n" ); document.write( "Let m1 = (-4/9)
\n" ); document.write( ":
\n" ); document.write( "Find the slope m2 from the given coordinates; x1=5, y1=-8; x2=9; y2=y:
\n" ); document.write( "m2 = \"%28%28y+-+%28-8%29%29%29%2F%28%289+-+5%29%29\" = \"%28%28y%2B8%29%29%2F4\"
\n" ); document.write( ":
\n" ); document.write( "We know the slope relationship of perpendicular lines is: m1 * m2 = -1
\n" ); document.write( "Substitute for m1 and m2:
\n" ); document.write( ":
\n" ); document.write( "\"%28-4%2F9%29%2A%28%28y%2B8%29%2F4%29\" = -1
\n" ); document.write( ":
\n" ); document.write( "Conveniently, the 4's cancel so we have:
\n" ); document.write( "\"-%28%28y%2B8%29%2F9%29\" = -1
\n" ); document.write( ":
\n" ); document.write( "\"%28%28y%2B8%29%2F9%29\" = +1; multiplied by -1
\n" ); document.write( ":
\n" ); document.write( "y + 8 = 9; multiplied equation by 9
\n" ); document.write( ":
\n" ); document.write( "y = 9 -8
\n" ); document.write( ":
\n" ); document.write( "y = 1
\n" ); document.write( ":
\n" ); document.write( "Therefore m2 = \"%28%28y%2B8%29%29%2F4\" = \"%28%281%2B8%29%29%2F4\" = \"9%2F4\" \n" ); document.write( "
\n" );