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15-Nov-09

Trigonometry

Use trigonometry to calculate an unknown side on

a right-angle triangle when you know an angle and

a side.

10 cm

?

350

900

B Grade Topic

Every angle has a sine (sin), cosine (cos) and

tangent (tan). You can obtain these from a

scientific calculator sin30 0.5

You will need to know the names of a right-angle

triangles sides.

h

hypotenuse

o

opposite

300

adjacent

a

You will need to know the rules for trigonometry

and these are often remembered by the saying,

soh cah toa This helps you to remember sine

opposite hypotenuse s o/h cosine

adjacent hypotenuse c a/h tangent

opposite adjacent t o/a The rules

show the relationship 2 6/3

v

v

s o/h c a/h t o/a 2 6/3

o

10 cm

h

x

v

?

v

x

300

900

a

Label the sides Write down the rules Tick what

you want Tick what you know Two ticks ? the

rule Use 2 6/3 to decide how to calculate

sin300 ?/10 0.5 ?/10 ? 0.5 x

10 ? 5 cm

x

v

s o/h c a/h t o/a 2 6/3

o

10 cm

h

v

v

v

x

300

900

a

?

Label the sides Write down the rules Tick what

you want Tick what you know Two ticks ? the

rule Use 2 6/3 to decide how to calculate

cos300 ?/10 0.8660 ?/10 ? 0.8660 x

10 ? 8.66 cm

v

v

s o/h c a/h t o/a 2 6/3

o

?

h

x

v

12 cm

x

v

300

900

a

Label the sides Write down the rules Tick what

you want Tick what you know Two ticks ? the

rule Use 2 6/3 to decide how to calculate

sin300 12/? 0.5 12/? ? 12

0.5 ? 24 cm

10 cm

1.

4.

?

?

8 cm

200

300

- 3.42
- 18.13
- 2.68
- 16
- 13.06
- 7.14

5.

20 cm

?

2.

250

400

10 cm

?

6.

3.

5 cm

?

350

150

?

10 cm