Question 860188
<pre><font face = "Tohoma" size = 3 color = "indigo"><b> 
Hi,
D(5, 7), 
E(4, 3) m = {{{ highlight_green(4)}}} DE = {{{sqrt(4^2 + 1^2)}}}
F(8, 2)m = {{{ highlight_green(-1/4)}}}  EF = {{{sqrt(1^2 + (-4)^2)}}}
DE perpendicular to EF and DE = EF
m DEF is  90° 
{{{drawing(300,300,   -10,10,-10,10, 
 grid(1),
circle(4,3,0.4),
circle(5,7,0.4),
circle(8,2,0.4),
line(4,3,5,7),
line(4,3,8,2),
line(5,7,8,2),
locate(5.3,7.8,"D"),
locate(3.6,2.6,"E"),
locate(8.3,2.8,"F"),
graph( 300, 300, -10,10,-10,10))}}}