# Trigonometry Basics | Maths with Lemon

Source: https://mathswithlemon.io/aa-geometry-trigonometry-Sin%20Cosine%20rules.html


## Trigonometry -Sine-Cosine Rules

"There is geometry in the humming of the strings, there is music in the spacing of the spheres. " Pythagoras


#### The sine, cosine and tangent of an angle in a triangle


##### What you have to know:

- You must be able to manipulate simple algebraic expressions. (If not, check this lesson)
- The Pythagorean theorem.

##### Key Points

- 1. Watch the video:
- 2. Read this presentation

#### The sine rule


##### What you have to know:

- The Pythagorean theorem.

##### Key Points

- 1. Watch the video:
- 2. Read this presentation

#### The cosine rule


##### What you have to know:

- The Pythagorean theorem.

##### Key Points

- 1. Watch the video:
- 2. Read this presentation

#### Area of a triangle


##### What you have to know:

- The Pythagorean theorem.

##### Key Points

- 1. Watch the video:
- 2. Read this presentation

#### Extra


##### Material and references:

- Hodder Book SL(ISBN: 9781510462359) : 18A

##### Key Points

- You should be able to convert between degrees and radians: \[ 360^\circ = 2\pi \text{ radians}. \]
- You should be able to find the length of an arc of a circle: \[ s = r\theta, \] where \( r \) is the radius of the circle and \( \theta \) is the angle subtended at the centre measured in radians.
- You should be able to find the area of a sector of a circle: \[ A = \tfrac{1}{2} r^2\theta, \] where \( r \) is the radius of the circle and \( \theta \) is the angle subtended at the centre measured in radians.

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