The length of AB would be 38 units
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Considering the triangle BCD;
Calculate the length BC using the following Pythagoras theorem
BC^2 = CD^2 + BD^2
This gives
BC^2 = 10^2 + 8^2
Evaluate
BC^2 = 164
Considering the triangle CBA;
Calculate the length AB using the following Pythagoras theorem
AB^2 = AC^2 - BC^2
This gives
AB^2 = 40^2 - 164
Evaluate
AB^2 = 1436
Take the square root
AB = 38 (approximated)
Hence, the length of AB would be 38 units
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