Mathematics Worksheet Section 8.4, 9.1, Study notes of Algebra

Solutions to problems related to finding the area of triangles and converting polar coordinates to rectangular coordinates. It also includes an application of finding the area of the Bermuda Triangle using the formula for the area of a triangle. from the Department of Mathematics at the University of Wisconsin-Madison and is for Math 114 course.

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Department of Mathematics, University of Wisconsin-Madison
Math 114
Worksheet Section 8.4, 9.1
1. Find the area of each triangle:
ab
c
C
BA
(a) a= 6, b= 4, C= 40.
Solution:
A=1
2ab sin 60
=1
2(6)(4) 3
2!
= 63
(b) a= 4, b= 5, c= 3.
Solution:
K=ps(sa)(sb)(sc)
s=1
2(a+b+c)
s=1
2(4 + 5 + 3)
s= 6
K=p6(6 4)(6 5)(6 3)
K=36
K= 6
1
pf3
pf4
pf5

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Department of Mathematics, University of Wisconsin-Madison

Math 114

Worksheet Section 8.4, 9.

  1. Find the area of each triangle:

b a

c

C

A B

(a) a = 6, b = 4, C = 40◦.

Solution:

A =

ab sin 60◦

(b) a = 4, b = 5, c = 3.

Solution:

K =

s(s − a)(s − b)(s − c)

s =

(a + b + c)

s =

s = 6

K =

K =

K = 6

  1. The Bermuda Triangle is roughly defined by Hamilton, Bermuda; San Juan, Puerto Rico; and Fort

Lauderdale, Florida. The distance from Hamilton to Fort Lauderdale, Fort Lauderdale to San Juan, and San Juan to Hamilton are approximately 1028, 1046, and 965 miles, respectively. Ignoring the curvature of Earth, approximate the area of the Bermuda Triangle.

Solution:

K =

s(s − a)(s − b)(s − c)

s =

(a + b + c)

s =

s = 1519. 5

K =

K ' 442 , 816 square miles

  1. In the following, polar coordinates of a point are given. Find the rectangular coordinate of each point.

(a)

3 π 2

Solution:

x = r cos θ

x = 4 cos

3 π 2

x = 0

y = r sin θ

y = 4 sin

3 π 2

y = − 4

Answer: (x, y) = (0, −4)

(b) (− 3 , 3)

Solution: The point is in the second quadrant so θ will be in the second quadrant.

r =

x^2 + y^2

r =

(−3)^2 + (3)^2

r = 3

tan θ =

y

x

tan θ =

tan θ = − 1

θ =

3 π

4

Answer: (r, θ) =

3 π

4

(c) (

Solution: The point is in the first quadrant so θ will be in the first quadrant.

r =

x^2 + y^2

r =

3)^2 + (1)^2

r = 2

tan θ =

y

x

tan θ =

θ =

π 6

Answer: (r, θ) =

π

6

  1. Write the equation x^2 + y^2 = x using polar coordinates.

Solution: x^2 + y^2 = r^2 and x = r cos θ So r^2 = r cos θ or r = cos θ

  1. Write the equation r = sin θ − cos θ using rectangular coordinates.

Solution:

r = sin θ − cos θ

r^2 = r sin θ − r cos θ

x^2 + y^2 = y − x