Answer: 5.4
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Step-by-step explanation:
Angle D = 43 is the given reference angle
side FE = 5 is the side opposite the reference angle (since its the leg furthest away from angle D)
We want to find side DE which is the other leg. This is the adjacent side with angle D as the reference angle
Use the tangent rule
tan(angle) = opposite/adjacent
tan(D) = FE/DE
tan(43) = 5/DE
DE*tan(43) = 5
DE = 5/tan(43)
DE = 5.36184355 <<-- use a calculator here; this is approximate
DE = 5.4 <<-- round to the nearest tenth
That's why 5.4 is the answer