(40-X)x(20+2X)= 1200

The solution is X 1= 10, X2=20 (omitted).

2. Set the hanging length x. ..

(4+2X)(6+2X)=2x4x6

The solution is X 1= 1, X2= -6 (abbreviated).

3. Make the midpoint Q of AB and connect FQ.

∵AF⊥FG

∴∠AFB+∠GFC=90

∠∠B = 90

∴∠FAB+∠AFB=90

∴∠FAB=∠GFC

∫CG bisection ∠ ∠DCM, ∠ DCF = 90.

∴∠QCF= 135

BF = BQ

∴∠FQA= 135

∫AQ = FC

∴△AFQ≌△FGC

∴AF=FG

4.5. Tuman?