HOW TO LABEL SIDES IN RIGHT ANGLED TRIANGLE TRIGONOMETRIC RATIOS BASICS GCSE MATHS YEAR 9 | PART I

GCSE Maths Trigonometry | Trigonometric ratios how to remember | Clear explanation

This is the first video dedicated to Trigonometric ratios and the main rules how to label sides of the right angle triangle correctly
I will also give the effective technique that allows you to memorize all trigonometric ratios much better than SOHCAHTO rule. It is more about understanding than just memorizing mnemonics. And also I will give you the way for proper calculations for angles and for inverse trigonometric functions that will ensure you that you are doing all correctly during ratios rearrangements


This is new series of videos dedicated to Trigonometry : GCSE Trigonometry . It doesn't include Further trigonometry, however this series will learn give you the best way ever to memorize trigonometric ratios and also you will learn how to apply it not only to MATH problems but also to Physics and to real life problems.

The playlist covers the following topics within trigonometry:

Correct Labelling sides of a right angled triangle
The trigonometric ratios
Problem solving
Applied Trigonometry
How to operate with the unit circle
True bearings
3-dimensional problem solving



Trigonometry is a branch of mathematics that deals with triangles. In particular, it considers the relationship between side lengths and angles in right-angled triangles. We can apply trigonometry everywhere: in engineering, astronomy, architecture, navigation, surveying, the building industry, and in many other branches of applied science.


For the right angled triangle with angle x (Degrees)

the hypotenuse (HYP) is the longest side
the opposite (OPP) side is opposite to the angle x
the adjacent (ADJ) side is adjacent to the angle x


For a particular angle of a right angled triangle the ratios
OPP/HYP, ADJ/HYP and OPP/ADJ are not changing.

These ratios have the traditional names sine, cosine and tangent respectively. We use shortcuts as sin, cos and tan.

Sometimes you need to find angle itself if you are given the ratios. In this case you can use graphics calculator (or GDC) or normal scientific calculator for finding these inverse trigonometric functions. We can define inverse cosine and inverse tangent in a similar way.


I will give you a bit of applications to science: we will discuss Hipparchus approach and actually you might find useful for your internal projects connected with exploration and discovery

Hipparchus was a Greek astronomer and mathematician born in Nicaea in the 2nd century BC. He is considered among the greatest astronomers of antiquity.

Problem 1: How Hipparchus measured the distance to the moon

Problem 2: How Hipparchus measured the radius of the moon

We also consider ANGLES OF ELEVATION AND DEPRESSION
The angle between the horizontal and your line of sight is called the angle of elevation if you are looking upwards, or the angle of depression if you are looking downwards.


When using trigonometry to solve problems we often use:

the properties of isosceles and right angled triangles
the properties of circles and tangents
angles of elevation and depression.


Problem Solving

The trigonometric ratios can be used to solve a wide variety of problems involving right angled triangles.
When solving such problems it is important to follow the instructions below:

Step 1: Read the question carefully.
Step 2: Draw a diagram, not necessarily to scale, with the given information clearly marked.
Step 3: If necessary, label the vertices of triangles in the figure.
Step 4: State clearly any assumptions you make which will enable you to use right angled triangles or properties of other geometric figures.
Step 5: Choose an appropriate trigonometric ratio and use it to generate an equation connecting the quantities. On some occasions more than one equation may be needed.
Step 6: Solve the equation(s) to find the unknown.
Step 7: Answer the question in words.



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