# Inter 1st Year Maths 1A Trigonometric Equations Formulas

Use these Inter 1st Year Maths 1A Formulas PDF Chapter 7 Trigonometric Equations Functions to solve questions creatively.

## Intermediate 1st Year Maths 1A Trigonometric Equations Formulas

→ If K ∈ [-1, 1], then the principal solution θ of sin θ = K lies in $$\left[\frac{-\pi}{2}, \frac{\pi}{2}\right]$$and the general solution is given by nπ + (-1)n θ, n ∈ Z

→ If K ∈ [-1, 1], then the principal solution θ of cos θ = K lies in [0, π] and the general solution is given by 2nπ ± 0, n ∈ Z

→ If K ∈ R, then the principal solution θ of tan x = K lies in $$\left(\frac{-\pi}{2}, \frac{\pi}{2}\right)$$, and the general solution is given by n\left(\frac{-\pi}{2}, \frac{\pi}{2}\right) ± θ, n ∈ Z

→ sin θ = 0 ⇒ θ = nπ, n is an integer and its principal solution is x = 0

→ cos θ = 0 ⇒ θ = (2n + 1)$$\frac{\pi}{2}$$, n is an integer and its principal solution is x = $$\frac{\pi}{2}$$

→ tan θ = 0 ⇒ θ = nπ, n is an integer and its principal solution is x = 0

→ cot θ = 0 ⇒ θ = (2n + 1)$$\frac{\pi}{2}$$ n is an integer

→ cosec θ = cosec α ⇒ θ = nπ + (-1)nα, n is an integer

→ sec θ = sec α ⇒ θ = 2nπ ± α, n is an integer

→ cot θ = cot α ⇒ θ = nπ ± α and the principal solution α ∈ (0, π)

→ sin2θ = sin2 α ⇒ θ = nπ ± α, wherenever a solution exists.

→ cos2θ = cos2 α ⇒ θ = nπ ± α, wherenever a solution exists.

→ tan2θ = tan2 α ⇒ θ = nπ ± α, wherenever a solution exists.

→ a cos θ + b sin θ = c, (a, b, c) ∈ R and a2 + b2 ≠ 0 has a solution, iff c2 ≤ a2 + b2.

Trigonometric Equations:
An equation consisting of the trigonometric functions of a variable angle θ ∈ R is called a trigonometric equation.

→ sin θ = 0 ⇒ θ = nπ, where n ∈ Z.

→ cos θ = 0 ⇒ θ = (2n + 1), where n ∈ Z.

→ tan θ = 0 ⇒ θ = nπ where π is any integer.

→ The solution of sin θ = k (|k|<1) lying between – $$\frac{\pi}{2}$$ and $$\frac{\pi}{2}$$ is called the principle solution of the equation.

→ The solution of cos θ = k (|k|<1) lying between 0 and π is called the principal solution of the equation.

→ That solution of tan θ = k, lying between – $$\frac{\pi}{2}$$ and $$\frac{\pi}{2}$$ is called the principal solution of the equation.

→ The general value of θ satisfying cos θ = k (|k| < 1) is given by θ = 2nπ ± α where n ∈Z.

→ The general value of θ satisfying sin θ = k (|k|< 1) is given by θ = nπ + (-1)nα where n ∈ Z.

→ The general value of θ satisfying tan θ = k is given by θ = nπ + α where n ∈ Z. (in each of the above cases, α is the principal solution).

→ If sin0 = k, tan0 = k are given equations, then the general value of θ is given by θ = 2nπ + α where α is that solution lying between 0 and 2π.

→ The equation a cos θ + b sin θ = c will have no solution or will be inconsistent if |c| > $$\sqrt{a^{2}+b^{2}}$$

→ cos nπ = (-1)n , sin nπ = 0.

→ If sin2θ = sin2α or cos2θ = cos2α or tan2θ = tan2a, then θ = nπ ± α; n ∈ Z.