Trigonometric Ratios
Trigonometric ratios are relationships between the angles and sides of a right-angled triangle. They are fundamental in solving geometric and real-world problems involving angles.
1. Defining Trigonometric Ratios
Consider a right-angled triangle with:
- Hypotenuse (r): The longest side opposite the right angle.
- Opposite (O): The side opposite the given angle θtheta.
- Adjacent (A): The side next to the given angle θtheta.
Primary Trigonometric Ratios
-
Sine (sin θ):
sin(θ) = Opposite / Hypotenuse = O / r -
Cosine (cos θ):
cos(θ) = Adjacent / Hypotenuse = A / r -
Tangent (tan θ):
tan(θ) = Opposite / Adjacent = O / A
Reciprocal Trigonometric Ratios
-
Cosecant (csc θ):
csc(θ) = 1 / sin(θ) = r / O -
Secant (sec θ):
sec(θ) = 1 / cos(θ) = r / A -
Cotangent (cot θ):
cot(θ) = 1 / tan(θ) = A / O
2. Trigonometric Ratios for Special Angles
Angle θtheta | sinθsin theta | cosθcos theta | tanθtan theta |
---|---|---|---|
0° | 0 | 1 | 0 |
30° | 12 1/2 | 32 + √3/2 | 13 + 1/√3 |
45° | 22 + √2/2 | 22 + (√2/2) | 1 |
60° | 32 + (√3/2) | 12 1/2 | 3√3 |
90° | 1 | 0 | Undefined |
3. Applications of Trigonometric Ratios
- Navigation & Aviation: Used to calculate angles and distances.
- Architecture & Engineering: Designing buildings and bridges.
- Physics & Astronomy: Measuring forces and celestial distances.
Waves
Amplitude
This is the maximum displacement of the wave above or below the x axis.
Period
The interval after which the wave repeats itself
Transformations of waves
The graphs of y = sin x and y = 3 sin x can be drawn on the same axis. The table below gives the corresponding values of sin x and 3 sin x for
Angle (°) | sin(x) | 3 sin(x) |
---|---|---|
0 | 0 | 0 |
30 | 0.50 | 1.50 |
60 | 0.87 | 2.61 |
90 | 1.00 | 3.00 |
120 | 0.87 | 2.61 |
150 | 0.50 | 1.50 |
180 | 0 | 0 |
210 | -0.50 | -1.50 |
240 | -0.87 | -2.61 |
270 | -0.50 | -1.50 |
300 | -0.87 | -2.61 |
330 | -0.50 | -1.50 |
360 | 0 | 0 |
390 | 0.50 | 1.50 |
420 | 0.87 | 2.61 |
450 | 1.00 | 3.00 |
480 | 0.87 | 2.61 |
510 | 0.50 | 1.50 |
540 | 0 | 0 |
570 | -0.50 | -1.50 |
600 | -0.87 | -2.61 |
630 | -1.00 | -3.00 |
660 | -0.87 | -2.61 |
690 | -0.50 | -1.50 |
720 | 0 | 0 |
The wave of y = 3 sin x can be obtained directly from the graph of y = sin x by applying a stretch scale
factor 3 , x axis invariant .
Note;
• The amplitude of y= 3sinx is y =3 which is three times that of y = sin x which is y =1.
• The period of the both the graphs is the same that is or 2
Example
Draw the waves y = cos x and y = cos . We obtain y = cos from the graph y = cos x by applying a stretch of factor 2 with y axis invariant.
Note;
• The amplitude of the two waves are the same.
• The period of y = cos is that is, twice the period of y = cos x