∠∠AGB = 90°, ∠ Gabe = 30.
∴AB=2GB=4,∠ABG=90-∠GAB=60
Square ABCD
∴CD=AB=4,∠ABC=90
∴∠CBG=∠ABC-∠ABG=90-60=30
∵GH⊥BC
∴gh=gb/2= 1,bh=gb×√3/2=2×√3/2=√3
∴CH=BC-BH=4-√3
∴CG? =GH? +CH? = 1+(4-√3)? =20-8√3
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