# 11.1 Graphs, trigonometric identities, and solving trigonometric

 Page 1 / 12

## History of trigonometry

Work in pairs or groups and investigate the history of the development of trigonometry. Describe the various stages of development and how different cultures used trigonometry to improve their lives.

The works of the following people or cultures can be investigated:

1. Cultures
1. Ancient Egyptians
2. Mesopotamians
3. Ancient Indians of the Indus Valley
2. People
1. Lagadha (circa 1350-1200 BC)
2. Hipparchus (circa 150 BC)
3. Ptolemy (circa 100)
4. Aryabhata (circa 499)
5. Omar Khayyam (1048-1131)
6. Bhaskara (circa 1150)
7. Nasir al-Din (13th century)
8. al-Kashi and Ulugh Beg (14th century)
9. Bartholemaeus Pitiscus (1595)

## Functions of the form $y=sin\left(k\theta \right)$

In the equation, $y=sin\left(k\theta \right)$ , $k$ is a constant and has different effects on the graph of the function. The general shape of the graph of functions of this form is shown in [link] for the function $f\left(\theta \right)=sin\left(2\theta \right)$ .

## Functions of the form $y=sin\left(k\theta \right)$

On the same set of axes, plot the following graphs:

1. $a\left(\theta \right)=sin0,5\theta$
2. $b\left(\theta \right)=sin1\theta$
3. $c\left(\theta \right)=sin1,5\theta$
4. $d\left(\theta \right)=sin2\theta$
5. $e\left(\theta \right)=sin2,5\theta$

Use your results to deduce the effect of $k$ .

You should have found that the value of $k$ affects the period or frequency of the graph. Notice that in the case of the sine graph, the period (length of one wave) is given by $\frac{{360}^{\circ }}{k}$ .

These different properties are summarised in [link] .

 $k>0$ $k<0$

## Domain and range

For $f\left(\theta \right)=sin\left(k\theta \right)$ , the domain is $\left\{\theta :\theta \in \mathbb{R}\right\}$ because there is no value of $\theta \in \mathbb{R}$ for which $f\left(\theta \right)$ is undefined.

The range of $f\left(\theta \right)=sin\left(k\theta \right)$ is $\left\{f\left(\theta \right):f\left(\theta \right)\in \left[-1,1\right]\right\}$ .

## Intercepts

For functions of the form, $y=sin\left(k\theta \right)$ , the details of calculating the intercepts with the $y$ axis are given.

There are many $x$ -intercepts.

The $y$ -intercept is calculated by setting $\theta =0$ :

$\begin{array}{ccc}\hfill y& =& sin\left(k\theta \right)\hfill \\ \hfill {y}_{int}& =& sin\left(0\right)\hfill \\ & =& 0\hfill \end{array}$

## Functions of the form $y=cos\left(k\theta \right)$

In the equation, $y=cos\left(k\theta \right)$ , $k$ is a constant and has different effects on the graph of the function. The general shape of the graph of functions of this form is shown in [link] for the function $f\left(\theta \right)=cos\left(2\theta \right)$ .

## Functions of the form $y=cos\left(k\theta \right)$

On the same set of axes, plot the following graphs:

1. $a\left(\theta \right)=cos0,5\theta$
2. $b\left(\theta \right)=cos1\theta$
3. $c\left(\theta \right)=cos1,5\theta$
4. $d\left(\theta \right)=cos2\theta$
5. $e\left(\theta \right)=cos2,5\theta$

Use your results to deduce the effect of $k$ .

You should have found that the value of $k$ affects the period or frequency of the graph. The period of the cosine graph is given by $\frac{{360}^{\circ }}{k}$ .

These different properties are summarised in [link] .

 $k>0$ $k<0$

## Domain and range

For $f\left(\theta \right)=cos\left(k\theta \right)$ , the domain is $\left\{\theta :\theta \in \mathbb{R}\right\}$ because there is no value of $\theta \in \mathbb{R}$ for which $f\left(\theta \right)$ is undefined.

The range of $f\left(\theta \right)=cos\left(k\theta \right)$ is $\left\{f\left(\theta \right):f\left(\theta \right)\in \left[-1,1\right]\right\}$ .

## Intercepts

For functions of the form, $y=cos\left(k\theta \right)$ , the details of calculating the intercepts with the $y$ axis are given.

The $y$ -intercept is calculated as follows:

#### Questions & Answers

a perfect square v²+2v+_
Dearan Reply
kkk nice
Abdirahman Reply
algebra 2 Inequalities:If equation 2 = 0 it is an open set?
Kim Reply
y=10×
Embra Reply
if |A| not equal to 0 and order of A is n prove that adj (adj A = |A|
Nancy Reply
rolling four fair dice and getting an even number an all four dice
ramon Reply
Kristine 2*2*2=8
Bridget Reply
Differences Between Laspeyres and Paasche Indices
Emedobi Reply
No. 7x -4y is simplified from 4x + (3y + 3x) -7y
Mary Reply
is it 3×y ?
Joan Reply
J, combine like terms 7x-4y
Bridget Reply
im not good at math so would this help me
Rachael Reply
how did I we'll learn this
Noor Reply
f(x)= 2|x+5| find f(-6)
Prince Reply
f(n)= 2n + 1
Samantha Reply
Need to simplify the expresin. 3/7 (x+y)-1/7 (x-1)=
Crystal Reply
. After 3 months on a diet, Lisa had lost 12% of her original weight. She lost 21 pounds. What was Lisa's original weight?
Chris Reply
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
can nanotechnology change the direction of the face of the world
Prasenjit Reply
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
Ali Reply
the Beer law works very well for dilute solutions but fails for very high concentrations. why?
bamidele Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
Got questions? Join the online conversation and get instant answers!
QuizOver.com Reply

### Read also:

#### Get the best Algebra and trigonometry course in your pocket!

Source:  OpenStax, Math 1508 (lecture) readings in precalculus. OpenStax CNX. Aug 24, 2011 Download for free at http://cnx.org/content/col11354/1.1
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Math 1508 (lecture) readings in precalculus' conversation and receive update notifications?

 By Anonymous User By Jordon Humphreys By