Question 230280
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We know two lines are perpendicular if they intersect and forms 90 deg.

{{{drawing(300,300,-5,5,-1,5,blue(line(-4,0,4,0)),line(0,0,0,4.2),green(line(0,.2,.4,.2)),green(line(.4,.2,.4,0)), green(locate(.5,.4,5x-12))))}}}


It follows, {{{5x-12=90^o}}}
{{{5x=90+12=102}}} ---> {{{cross(5)x/cross(5)=cross(102)20.4/cross(5)}}}
{{{green(x=20.4^o)}}}, Answer


Thank you,
Jojo</font>