What Are the Correct Tension Forces in Cables Lifting a 8Mg Tractor?

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A tank hanging off a hook, what are the tension forces?

Homework Statement


2ahvas4.jpg

Determine the forces in cables AB, AC and AD needed to lift the tractor which has a mass of 8Mg.


Homework Equations





The Attempt at a Solution


I found the unit vectors of the three rope forces using the ropes' position vectors.

B = [-0.5241i -0.3276j -0.7861k]
C = [-0.5241i 0.3276j -0.7861k]
D = [0.31623i 0j -0.9487k]

So F_B = -9.8bB, F_C = -9.8cC and F_D = -9.8dD where b, c, d = magnitudes of the forces

Then I set up a system of equations to find b, c and d. I found:
b = c = -1.691Mg
d = -5.6218Mg

|F_b| = |F_c| = 9.8*1.691E6 = 1.66E7 N
|F_d| = 9.8*5.6218E6 = 5.51E7 N

But I checked and they aren't the right answers. What did I do wrong?
 
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