From the setup of the problem, the "length of the top of the bookcase, measured along the attic ceiling" will be the hypotenuse of a right triangle, the length "AB". We have both the angle between AB and AC and the length of AC (3.24 meters), so we can use trigonometric identities.
The cosine of the 40 degree angle between AB and AC is equivalent to the length of AC divided by the length of AB. Equivalently, we have:

where "h", the hypotenuse, is the length we want. Rearranging the formula to solve for h we have that

which is 4.2295... meters. Converting to centimeters (multiplying by 100) we have that h = 422.95... centimeters, or if we round the value, h = 423 centimeters.
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Answer:<em> X=6</em></h2>
Hope this is the answer you are looking for.. if it's wrong please letme know
Answer:
6 mm
Step-by-step explanation:
Use the Pythagorean Theorem to solve for the unknown leg

Since we need to solve for a, we will manipulate the equation in terms of b and c → 
Here, b = 7 mm and c =
mm
Plugging these numbers into our equation gives us
→
=
= 6 mm
Answer:
Multiply by two. Formula could be x * 2
Step-by-step explanation: