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Mathematics 93 13 implication
① ② is the special feature of ③. Direct proof (3) Take the coordinate system as shown in the figure and let d (0 0,0) and c (2 2,0).

B(2,2),A(0,2)。 Let F(2a, 2b), then M(a, b)[DF midpoint], N(-b, a)[ square].

E(a-b,a+b)。 G(a+ 1,b+ 1)。

CG slope = (b+ 1)/(a- 1). EG slope = (1-a)/( 1+b),

∵[(b+ 1)/(a- 1)]×[( 1-a)/( 1+b)]=- 1∴cg⊥eg.

CG & ampsup2=(a- 1)amp; sup2+(b+ 1)& amp; sup2。 ? EG & ampsup2=(-b- 1)& amp; sup2+(a- 1); sup2。

∫(a- 1) and AMPSUP2+(b+1)&; sup2=(-b- 1)& amp; sup2+(a- 1); sup2。 ∴CG=EG.