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## Trigonometry

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### Instant Trig Trigonometry is math, ... there are six ways to divide the lengths of the sides Each of these six ratios has a name (and an abbreviation) ... – PowerPoint PPT presentation

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Title: Trigonometry

1
Trigonometry
• Introduction

2
Instant Trig
• Trigonometry is math, so many people find it
scary
• Its usually taught in a one-semester high-school
course
• However, 95 of all the trig youll ever need
to know can be covered in 15 minutes
• And thats what were going to do now

3
Angles add to 180
• The angles of a triangle always add up to 180

4
Right triangles
• We only care about right triangles
• A right triangle is one in which one of the
angles is 90
• Heres a right triangle

Heres the right angle
hypotenuse
opposite
adjacent
• We call the longest side the hypotenuse
• We pick one of the other angles--not the right
angle
• We name the other two sides relative to that angle

5
The Pythagorean Theorem
• If you square the length of the two shorter sides
and add them, you get the square of the length of
the hypotenuse
• adj2 opp2 hyp2
• 32 42 52, or 9 16 25
• hyp sqrt(adj2 opp2)
• 5 sqrt(9 16)

6
5-12-13
• There are few triangles with integer sides that
satisfy the Pythagorean formula
• 3-4-5 and itsmultiples (6-8-10, etc.)are the
best known
• 5-12-13 and its multiples form another set
• 25 144 169

7
Ratios
• Since a triangle has three sides, there are six
ways to divide the lengths of the sides
• Each of these six ratios has a name (and an
abbreviation)
• Three ratios are most used
• sine sin opp / hyp
• cosine cos adj / hyp
• tangent tan opp / adj
• The other three ratios are redundant with these
and can be ignored
• The ratios depend on the shape of the triangle
(the angles) but not on the size

8
Using the ratios
• With these functions, if you know an angle (in
addition to the right angle) and the length of a
side, you can compute all other angles and
lengths of sides
• If you know the angle marked in red (call it A)
and you know the length of the adjacent side,
then
• tan A opp / adj, so length of opposite side is
given by opp adj tan A
• cos A adj / hyp, so length of hypotenuse is
given by hyp adj / cos A

9
The Hard Part
• If you understood this lecture, youre in great
shape for doing all kinds of things with basic
graphics
• Heres the part Ive always found the hardest
• Memorizing the names of the ratios
• sin opp / hyp
• cos adj / hyp
• tan opp / adj

10
Mnemonics from wikiquote
• The formulas for right-triangle trigonometric
functions are
• Sine Opposite / Hypotenuse
• Cosine Adjacent / Hypotenuse
• Tangent Opposite / Adjacent
• Mnemonics for those formulas are
• Some Old Horse Caught Another Horse Taking Oats
Away
• Saints On High Can Always Have Tea Or Alcohol
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