Grade 12 ↓
Advanced Trigonometry
Trigonometry is a branch of mathematics that studies relationships involving side lengths and angles of triangles. In advanced trigonometry, we delve deeper into the properties and applications of trigonometric functions beyond the basic right triangle relationships.
Trigonometric functions and their definitions
The elementary trigonometric functions are sine (sin
), cosine (cos
), and tangent (tan
). These functions are traditionally defined as the ratios of the sides of a right triangle:
sin(θ) = (frac{text{opposite}}{text{hypotenuse}})
cos(θ) = (frac{text{adjacent}}{text{hypotenuse}})
tan(θ) = (frac{text{opposite}}{text{adjacent}})
The inverses of these functions are cosecant (csc
), secant (sec
), and cotangent (cot
):
csc(θ) = (frac{1}{sin(θ)})
sec(θ) = (frac{1}{cos(θ)})
cot(θ) = (frac{1}{tan(θ)})
Unit circle and radian measure
The unit circle is a fundamental part of trigonometry. It is a circle with radius one, centered at the origin in the coordinate plane. Angles in radians are an alternative way to measure angles, where the angle is defined as the length of the arc that subtends the angle at the center of a circle with radius one.
1 radian is approximately equal to 57.2958 degrees. An angle measured in radians is given by:
Angle (in radians) = (frac{text{Arc length}}{text{Radius}})
Trigonometric identities
Trigonometric identities are equations that are true for any value of the variable where both sides of the equation are defined. These identities are useful in simplifying expressions or solving equations.
- Pythagorean identity
sin²(θ) + cos²(θ) = 1
1 + tan²(θ) = sec²(θ)
1 + cot²(θ) = csc²(θ)
- Angle sum and difference identities
sin(α ± β) = sin(α)cos(β) ± cos(α)sin(β)
cos(α ± β) = cos(α)cos(β) ∓ sin(α)sin(β)
tan(α ± β) = (frac{tan(α) ± tan(β)}{1 ∓ tan(α)tan(β)})
Example: Proving an identity
Let us consider the identity sin(2θ) = 2sin(θ)cos(θ)
.
- Start with the angle sum identity for sine:
sin(α + β) = sin(α)cos(β) + cos(α)sin(β)
- Set
α = β = θ
: - It's simple:
sin(2θ) = 2sin(θ)cos(θ)
sin(θ + θ) = sin(θ)cos(θ) + cos(θ)sin(θ)
Graphing trigonometric functions
The graphs of trigonometric functions are periodic. This means that they repeat values at regular intervals or periods. Understanding the basic shape of these graphs helps in understanding their behavior.
Sine and cosine graphs
Sine and cosine functions have amplitudes (the height of their peaks), periods (the length of time before they start repeating), and phases (the shift along the x-axis).
Tangent graph
The tangent function has a period of π and has vertical asymptotes, where the function is undefined.
Inverse trigonometric functions
The inverse trigonometric functions are used to find the angle corresponding to a given trigonometric ratio. For example, if sin(θ) = 0.5
, then θ = sin -1 (0.5)
.
sin -1 (x)
where-1 ≤ x ≤ 1
cos -1 (x)
for-1 ≤ x ≤ 1
tan -1 (x)
for all real numbers
Solving trigonometric equations
Solving trigonometric equations often involves using identities and algebraic manipulation to find the angles that satisfy the equation.
Example: Solve 2sin(θ) - 1 = 0
for 0 ≤ θ < 2π
- Add 1 to both sides:
2sin(θ) = 1
- Divide by 2:
sin(θ) = 0.5
- Find θ:
θ = sin -1 (0.5)
- Possible solution:
θ = (frac{π}{6}) or (frac{5π}{6})
Applications of trigonometry
Trigonometry is widely used in various fields such as physics, engineering, astronomy and architecture. Here are some applications:
- Physics: Calculating models of wave motion, oscillations, and periodic phenomena.
- Engineering: Design and analysis of mechanical structures, electrical circuits, and signal processing.
- Astronomy: Measuring distances between stars and understanding celestial mechanics.
- Architecture: Designing roofs, bridges and other structures that involve angles and distances.