Answer:

Step-by-step explanation:
In rectangle ABCD, AB = 6, BC = 8, and DE = DF.
ΔDEF is one-fourth the area of rectangle ABCD.
We want to determine the length of EF.
First, we can find the area of the rectangle. Since the length AB and width BC measures 6 by 8, the area of the rectangle is:

The area of the triangle is 1/4 of this. Therefore:

The area of a triangle is half of its base times its height. The base and height of the triangle is DE and DF. Therefore:

Since DE = DF:

Thus:

Since ABCD is a rectangle, ∠D is a right angle. Then by the Pythagorean Theorem:

Therefore:

Square:

Add:

And finally, we can take the square root of both sides:

Answer:
AC = 12.38 cm
Step-by-step explanation:
When there are 2 pairs given, we can use the sine rule to solve the problem.
By pairs we mean "an angle and side opposite to it"
<em>1 pair is 85.2 degree angle and 13 cm, and another pair is 71.6 degree angle and the side AC (which we want to figure out).</em>
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Sine Rule is given by 
where,
A and B are the two respective angles and a and b are the two respective sides (of the pairs). Plugging all the info and using algebra, we have:

Thus, AC = 12.38 cm
Answer:c
Step-by-step explanation:
C