WELCOME TO ALG. 2A

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TODAY’S AGENDA

This Week at a Glance

Return Ch. 13 Quizzes

13.5A Notes

Assignment: 13.5 Skills Practice

THIS WEEK AT A GLANCE

Monday: 13.5A Law of Cosines

Tuesday: 13.5B Law of Cosines

Wednesday: Ch. 13A Review

Thursday: Ch. 13A Test

Friday: Begin Ch. 13B ~ Unit

Circle

CH. 13A QUIZ

2) Write an equation involving sine, cosine, or tangent that can be used to find x. Then solve the equation, rounding to the nearest degree.

CH. 13A QUIZ

Solve

3) Solve ∆ABC if mA = 20, mC = 90, and b = 10. Round measures of sides to the nearest tenth and measures of angles to the nearest degree.

CH. 13A QUIZ

4) Using the Law of Sines, find the measure of angle A when c = 15, mB = 50, and b = 12.4.

A

B

C

LESSON 13.5A

I CAN . . .

· solve problems by using Law of Cosines.

VOCABULARY

Term Definition Example

Law of Cosines

In any ABC,

Use Law of Sines when given

_______, or _______.

SASSS

S

cA

C

a

B

b

a2 = b2 + c2 – 2bc cos A

b2 = a2 + c2 – 2ac cos B

c2 = a2 + b2 – 2ab cos C

EXAMPLE 1:

In ABC, find c.

Cabbac cos2222

2c 22 1210 48cos

2c 4.83

12102

1.9c

EXAMPLE 2:

In ABC, find r.

Cabbac cos2222

2c 22 1412 62cos2c 3.182

14122

5.13c

r

EXAMPLE 3:

A ranger tower at point A is directly north of a ranger tower at point B. A fire

at point C is observed from both towers. The distance from the fire to tower A is

60 miles, and the distance from the fire to tower B is 50 miles. If mACB = 62,

find the difference between the towers.

A

B

C

50

62

60

c

Cabbac cos2222

62cos605026050 222 c

2.32832 c

3.57c

TODAY’S ASSIGNMENT

13.5 Skills Practice

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