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# 1-1 Using Trigonometry to Find Lengths - PowerPoint PPT Presentation

1-1 Using Trigonometry to Find Lengths. You have been hired to refurbish the Weslyville Tower… (copy the diagram, 10 lines high, the width of your page.). In order to bring enough gear, you need to know the height of the tower……. How would you determine the tower’s height?.

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### 1-1Using Trigonometry to Find Lengths

You have been hired to refurbish the Weslyville Tower…(copy the diagram, 10 lines high, the width of your page.)

In order to bring enough gear, you need to know the height of the tower……

How would you determine the tower’s height?

Imagine the sun casting a shadow on the ground. to be useful.

Turn this situation into a right angled triangle

The length of the shadow can be measured directly to be useful.

The primary angle can also be measured directly

X

The Height?

Sooo…

40O

200 m

Make a model!! to be useful.

Draw a right angled triangle with a base of 20 cm and a primary angle of 40O, then just measure the height!

X cm to be useful.

=

20 000 cm

We can generate an equation using equivalent fractions to determine the actual height!

General Model Real

X cm

Height

17 cm

=

=

Base

20 000 cm

20 cm

0.85

20 000 (0.85) = X

170 m = X

In the interest of efficiency.. to be useful.

• Drawing triangles every time is too time consuming.

• Someone has already done it for us, taken all the measurements, and loaded them into your calculator

• Examine the following diagram

O to be useful.

O

O

O

As the angle changes, so

shall all the sides

of the triangle.

Recall the Trig names for different sides of a triangle…

Geometry to be useful.

hypotenuse

height

O

base

Trigonometry

hypotenuse

opposite

“theta”

Aryabhata (Hindu) began to study specific ratios.

For the ratio OPP/HYP, the word “Jya” was used

Brahmagupta, in 628, continued studying the same relationship and“Jya” became “Jiba”

“Jiba became Jaib”which means “fold” in arabic

European Mathmeticians translated “jaib” into latin: relationship and

SINUS

(later compressed to SIN by Edmund gunter in 1624)

Given a right triangle, the 2 remaining angles must total 90 relationship andO.

A = 10O, then B = 80O

A = 30O, then B = 60O

A

A “compliments” B

C

B

The ratio ADJ/HYP compliments the ratio OPP/HYP in the similar mathematical way.

Therefore, ADJ/HYP is called “Complimentary Sinus”

COSINE

The 3 Primary Trig Ratios similar mathematical way.

SINO = opp

O

hyp

hyp

hyp

opp

TANO = opp

soh cah toa similar mathematical way.

1

A

X 17

FIND A:

17 X

COS25O =

17

1

A = 17 X cos25O

17m

A = 15.4 m

25O

A

soh cah toa similar mathematical way.

1

A

X 12

FIND A:

12 X

SIN32O =

12

1

A = 12 X SIN32O

12 m

A = 6.4 m

A

32O

soh cah toa similar mathematical way.

1

A

X 10

FIND A:

10 X

TAN63O =

10

1

A = 10 X TAN63O

63O

A = 19.6 m

10 m

A

X similar mathematical way.

Tan 40O =

200

200 (Tan40O) = X

168 m = X

X

40O

200 m

Remember: Equivalent fractions can be inverted similar mathematical way.

2

5

=

4

10

4

10

=

2

5

Page 8 similar mathematical way.

[1,2] a,c

3-7

TAN 50 = H similar mathematical way.

150

1

150 X

X 150

1

(150) TAN 50 = H

HYP

OPP

H

150 m