document.write( "Question 216996: Find k that so that the line through (4,4) and (k,8) is
\n" ); document.write( "a) parallel to 3y-4x=7
\n" ); document.write( "b) perpendicular to 4y+5x=1 \n" ); document.write( "
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a )
\n" ); document.write( "parallel = same grad
\n" ); document.write( "3y= 7+4x
\n" ); document.write( "make y the subject
\n" ); document.write( "y= 7/3 + 4/3x
\n" ); document.write( "grad = 4/3\r
\n" ); document.write( "\n" ); document.write( "grad of line through (4,4) and (k,8) . leave k as it is
\n" ); document.write( "grad = 4-8 / 4-k
\n" ); document.write( "4/3 = -4 / 4-k
\n" ); document.write( "cross multiply it ,
\n" ); document.write( "16-4k=-12
\n" ); document.write( "16+12 = 4k
\n" ); document.write( "k = 7 (ans)\r
\n" ); document.write( "\n" ); document.write( "b)
\n" ); document.write( "perpendicular = negative reciprocal
\n" ); document.write( "4y+5x=1
\n" ); document.write( "make y the subject always.
\n" ); document.write( "4y=1-5x
\n" ); document.write( "y= 1/4 - 5/4x
\n" ); document.write( "grad= -5/4
\n" ); document.write( "perpendicular grad = 4/5 \r
\n" ); document.write( "\n" ); document.write( "from previous steps , -4/4-k is the grad so ,
\n" ); document.write( "4/5 = -4/4-k
\n" ); document.write( "cross multiply ,
\n" ); document.write( "16 - 4k = -20
\n" ); document.write( "16+20 = 4k
\n" ); document.write( "k = 9 (ans)
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