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through (2,5) and parallel to 2x+4y=8
\n" ); document.write( "i don't know how to change 2x+4y=8 into a form so that i can graph it.
\n" ); document.write( "2x + 4y = 8 is a straight line, so only 2 points are needed.
\n" ); document.write( "Change it to slope-intercept form y = mx + b (that means solve for y).
\n" ); document.write( "x + 2y = 4
\n" ); document.write( "2y = -x + 4
\n" ); document.write( "y = (-1/2)x + 2
\n" ); document.write( "The slope, m, = -1/2 and the y-intercept is b.
\n" ); document.write( "All lines parallel have the same slope.
\n" ); document.write( "Now, find the equation of the line thru (2,5) with a slope of -1/2.
\n" ); document.write( "Use y = mx+b
\n" ); document.write( "5 = (-1/2)*2 + b
\n" ); document.write( "b = 6
\n" ); document.write( "--> y = (-1/2)x + 6
\n" ); document.write( "or x + 2y = 12
\n" ); document.write( "--------------------
\n" ); document.write( "the other one is:
\n" ); document.write( "through (2,5) and perpendicular to 2x+4y=8
\n" ); document.write( "The slope of lines perpendicular is the negative inverse of -1/2, so
\n" ); document.write( "m = +2
\n" ); document.write( "5 = 2*2 + b
\n" ); document.write( "b = 1
\n" ); document.write( "y = 2x + 1 is perpendicular thru (2,5)
\n" ); document.write( "--------------
\n" ); document.write( "To graph these, find 2 points.
\n" ); document.write( "y = 2x+1
\n" ); document.write( "Pick 2 values for x and find y
\n" ); document.write( "x = 0, y = 1
\n" ); document.write( "x = 3, y = 7
\n" ); document.write( "(0,1) and (3,7)
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