Answer:
87.73 inches
Step-by-step explanation:
We are given that the dimensions of the rectangular doorway are,
Length = 6 ft 8 inches = 80 inches and Width = 3 feet = 36 inches.
Using Pythagoras Theorem, we will find the diagonal of the rectangular doorway.
i.e. 
i.e. 
i.e. 
i.e. 
i.e. Hypotenuse = ±87.73 inches
Since, the length cannot be negative.
So, the length of the diagonal is 87.73 inches.
As, the largest side of a rectangle is represented by the diagonal.
So, the largest dimension that will fit through the doorway without bending is 87.73 inches.
None of these. All of these functions are defined as ratio of trigonometric functions.
Trigonometric functions have infinite zeroes, so when you put them in the denominator, they lead to infinitely many points of ill-definition.
Specifically, we have:

which is undefined at


which is undefined at


which is undefined at


which is undefined at

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