Answer:
16. Angle C is approximately 13.0 degrees.
17. The length of segment BC is approximately 45.0.
18. Angle B is approximately 26.0 degrees.
15. The length of segment DF "e" is approximately 12.9.
Step-by-step explanation:
<h3>16</h3>
By the law of sine, the sine of interior angles of a triangle are proportional to the length of the side opposite to that angle.
For triangle ABC:
,- The opposite side of angle A
, - The angle C is to be found, and
- The length of the side opposite to angle C
.
.
.
.
Note that the inverse sine function here
is also known as arcsin.
<h3>17</h3>
By the law of cosine,
,
where
,
, and
are the lengths of sides of triangle ABC, and
is the cosine of angle C.
For triangle ABC:
,
, - The length of
(segment BC) is to be found, and - The cosine of angle A is
.
Therefore, replace C in the equation with A, and the law of cosine will become:
.
.
<h3>18</h3>
For triangle ABC:
,
,
, and- Angle B is to be found.
Start by finding the cosine of angle B. Apply the law of cosine.
.
.
.
<h3>15</h3>
For triangle DEF:
- The length of segment DF is to be found,
- The length of segment EF is 9,
- The sine of angle E is
, and - The sine of angle D is
.
Apply the law of sine:

.
I think you want to prove that a rectangle is a quadrilateral. You can prove this with definitions. The definition of a quadrilateral is that it is a shape with four sides. Since a rectangle has four sides, that proves that a rectangle is a quadrilateral.
The item would cost approximately $45. You can do this by taking the price of the item ($60) and multiply by the percent (25%). 60 x 0.25 = 15. That is the discount you would subtract from the item itself. Now you would take the original price ($60) and subtract the discount ($15). 60 - 15 = 45.