Billy collects marbles. Each marble in his collection weighs about 4 ounces. His collection weighs about 20 pounds in all. About
1 answer:
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Answer:
16.2
Step-by-step explanation:
The angle internal to the triangle at B is the supplement of the one shown, so is 65°. That is equal to the angle internal to the triangle at D. Since the vertical angles at C are congruent, the two triangles are similar by the AA theorem.
Corresponding sides of similar triangles are proportional, so we can write the proportion shown in the attachment:
BC/FC = DC/AC
BC = FC(DC/AC) = 21.6(7.2/9.6)
BC = 16.2 . . . . matches the first choice
We will use the sine and cosine of the sum of two angles, the sine and consine of 
, and the relation of the tangent with the sine and cosine:
If you use those identities, for
, you get:
Hence:
If you use those identities, for
Hence: