77. Since GAexerts a leftward force Tat the corner A, then (by equilibrium of horizontal forces at that point) the force Fdiagin CAmust be pulling with magnitude diag2.sin 45TFT==°This analysis applies equally well to the force in DB. And these diagonal bars are pulling on the bottom horizontal bar exactly as they do to the top bar, so the bottom bar CDis the “mirror image” of the top one (it is also under tension T). Since the figure is symmetrical (except for the presence of the turnbuckle) under 90° rotations, we conclude that the side
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