Sine Rule and Cosine Rule

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# Sine Rule and Cosine Rule - PowerPoint PPT Presentation

Sine Rule and Cosine Rule. Clicker Practice. SOH/CAH/TOA can only be used for right-angled triangles. The Sine Rule can be used for any triangle:. a sin A. b sin B. c sin C. = =. C. b. The sides are labelled to match their opposite angles. a. A. B. c. The Sine Rule:.

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### Sine Rule and Cosine Rule

Clicker Practice

SOH/CAH/TOA can only be used for right-angled triangles.

The Sine Rule can be used for any triangle:

a

sinA

b

sinB

c

sinC

= =

C

b

The sides are labelled to match their opposite angles

a

A

B

c

The Sine Rule:

We use the Sine Rule when:

We have two angles and a side

OR

We have two sides and the non-included angle (this is the ambiguous case)

Find the length of a in cm.
• 5.53
• 0

B

53º

3 sig figs!!

62º

A

5 cm

C

Find the measure of angle EDF:
• 57.7
• 0

D

8 m

θ

3 sig figs!!

F

70º

9.5 m

E

We use the Cosine Rule when:

Two sides and the INCLUDED angle (SAS)

OR

All three sides (SSS)

The Cosine Rule

A

c

b

B

C

a

B

C

(One side)2

=

(other side)2+(last side)2

-

2(other side)(last side)cos(angle of 1st side)