Use these Inter 1st Year Maths 1A Formulas PDF Chapter 8 Inverse Trigonometric Functions to solve questions creatively.

Intermediate 1st Year Maths 1A Inverse Trigonometric Functions Formulas

→ If sin θ = x and θ ∈ \(\left[\frac{-\pi}{2}, \frac{\pi}{2}\right]\), then sin-1(x) = θ,

→ If cos θ x and θ ∈ [0, π], then cos-1(x) = θ

→ If tan θ = x and θ ∈ \(\left(\frac{-\pi}{2}, \frac{\pi}{2}\right)\). then tan-1 (y) = θ

→ If cot θ = x and θ ∈ (0, π), then cot-1(x) = θ.

→ If sec θ = x and θ ∈ [o, \(\frac{\pi}{2}\)) ∪ (\(\frac{\pi}{2}\), π] then sec-1x = θ.

→ If cosec θ = x and θ ∈ [-\(\frac{\pi}{2}\), 0) ∪ (o, \(\frac{\pi}{2}\)] then cosec-1x = θ.

→ If x ∈ [-1, 1] – {0}, then sin-1(x) = cosec-1\(\left(\frac{1}{x}\right)\)

Inter 1st Year Maths 1A Inverse Trigonometric Functions Formulas

→ If x ∈ [-1, 1] – {0}, then cos-1(x) = sec-1\(\left(\frac{1}{x}\right)\)

→ If x > 0, then tan-1(x) = cot-1\(\left(\frac{1}{x}\right)\) and
x < 0, then tan-1(x) = cot-1\(\left(\frac{1}{x}\right)\) – π

→ sin-1 x + cos-1x = \(\frac{\pi}{2}\) (|x| ≤ 1) i.e., – 1 ≤ x ≤ 1

→ tan-1x + cot-1x = \(\frac{\pi}{2}\), for any x ∈ R

→ sec-1x + cosec-1x = \(\frac{\pi}{2}\), if (-∞, – 1] ∪ [1, ∞)

Function y = f(x) Domain (x) Range (y)
(i) sinh-1 (x) [-1, 1] \( \left[\frac{-\pi}{2}, \frac{\pi}{2}\right] \)
(ii) cosh-1 (x) [1, 1] [0, π]
(iii) tanh-1 (x) R \( \left(\frac{-\pi}{2}, \frac{\pi}{2}\right) \)
(iv) cot-1 (x) R (0, π)
(v) sec-1 (x) (-∞, -1] ∪ [1, ∞) [0, \( \frac{\pi}{2} \)) ∪ (\( \frac{\pi}{2} \), π]
(vi) cosec-1 (x) (-∞, -1] ∪ [1, ∞) [-\( \frac{\pi}{2} \), 0) ∪  (0, \( \frac{\pi}{2} \), π]

→ Principal values:
For sin-1x, tan-1x, cot-1x, cosec-1x, principal values lies between –\(\frac{\pi}{2}\) and \(\frac{\pi}{2}\)
For cos-1 x, sec-1 x, principal values lies between 0 and π.

→ tan-1x + tan-1y = tan-1\(\left(\frac{x+y}{1-x y}\right)\) if (xy < 1), x > 0, y > 0
= \(\frac{\pi}{2}\) if (xy = 1), x > 0, y > 0
= π +tan-1\(\), if (xy > 1), x > 0, y > 0

→ If x < 0, y < 0 then tan-1x + tan-1y = tan-1\(\left(\frac{x+y}{1-x y}\right)\) if xy > 1
= – \(\frac{\pi}{2}\), if xy < 1
= –\(\frac{\pi}{2}\), if xy = 1

→ If x, y ∈ [0, 1] and x2 + y2 ≤ 1, then sin-1 x + sin-1 y = sin-1\(\left(x \sqrt{1-y^{2}}+y \sqrt{1-x^{2}}\right)\)

→ If x, y ∈ [0, 1] and x2 + y2 > 1 then sin-1 x + sin-1 (y) = π – sin-1\(\left(x \sqrt{1-y^{2}}+y \sqrt{1-x^{2}}\right)\)

→ If x, y ∈ [0, 1], then sin-1 x + sin-1y) = cos-1(\(\sqrt{1-x^{2}} \sqrt{1-y^{2}}\) – xy)

→ If x, y ∈ [0, 1] then sin-1 y = sin-1(x\(\sqrt{1-y^{2}}\) – y\(\sqrt{1-x^{2}}\))

Inter 1st Year Maths 1A Inverse Trigonometric Functions Formulas

→ If x, y ∈ [0, 1], then cos-1 x + cos-1y = cos-1(\(\sqrt{1-x^{2}} \sqrt{1-y^{2}}\) + xy)

→ If x, y ∈ [0, 1] then cos-1 x + cos-1y = cos-1(xy – \(\sqrt{1-x^{2}} \sqrt{1-y^{2}}\))

→ If x, y ∈ [0, 1] and x2 + y2 ≥ 1 then cos-1x + cos-1y = sin-1(y\(\sqrt{1-x^{2}}\) + x\(\sqrt{1-y^{2}}\))

→ If 0 ≤ x ≤ y ≤ 1 then cos-1 x – cos-1y = cos-1(xy + \(\sqrt{1-x^{2}} \sqrt{1-y^{2}}\))

→ If x, y ∈ [0, 1], then cos-1 x – cos-1y = sin-1(y\(\sqrt{1-x^{2}}\) – x\(\sqrt{1-y^{2}}\))

→ If x ∈ [-1, 1]- {0}, then sin-1 (x) = cosec-1\(\left(\frac{1}{x}\right)\)

→ If x ∈ [-1, 1] – {0}, then cos-1(x) = sec-1\(\left(\frac{1}{x}\right)\)

→ If x > 0, then tan-1x = cot-1\(\left(\frac{1}{x}\right)\) and

→ If x < 0, then tan-1x = cot-1\(\left(\frac{1}{x}\right)\) – π

→ sin-1(-x) = -sin-1(x), if x ∈ [-1, 1]

→ cos-1(-x) = π – cos-1(x), if x ∈ [-1, 1]

→ tan-1(-x) = -tan-1 (x), for any x ∈ R

→ For any x ∈ R, cot-7 (-x) = π – cot-1(x)

→ If x ∈ [-∞, -1] ∪ [1, ∞) then

  • sec-1(-x) = π – sec-1(x)
  • cosec-1(-x) = -cosec-1(x)

Inter 1st Year Maths 1A Inverse Trigonometric Functions Formulas

→ If θ ∈ \(\left[-\frac{\pi}{2}, \frac{\pi}{2}\right]\), then sin-1(sin θ) = θ and if x ∈ [-1, 1], then sin(sin-1x) = x.

→ If θ ∈ [0, π], then cos-1(cos θ) = θ and if x ∈ [-1, 1], then cos (cos-1x) = x.

→ If θ ∈ \(\left(-\frac{\pi}{2}, \frac{\pi}{2}\right)\), then tan-1(tan θ) = θ and for any x ∈ R, then tan(tan-1x) = x

→ If θ ∈ (0, \(\frac{\pi}{2}\)) ∪ (\(\frac{\pi}{2}\), π) then cot-1(cot θ) = θ and for any x ∈ R, cot (cot-1x) = x.

→ If θ ∈ (0, \(\frac{\pi}{2}\)) ∪ (\(\frac{\pi}{2}\), π) then sec-1(sec θ) = θ and if x ∈ (-∞, -1] ∪ [1, ∞) then sec (sec-1x) = x.

→ If θ ∈ [-\(\frac{\pi}{2}\), 0) ∪ (0, \(\frac{\pi}{2}\)] then cosec-1 (cosec θ) = θ and if x ∈ (-∞, -1] ∪ [1, ∞), then cosec (cosec-1x) = x.

→ θ ∈ [0, π] sin-1(cos θ) = \(\frac{\pi}{2}\) – θ

→ θ ∈ \(\left[\frac{\pi}{2}, \frac{\pi}{2}\right]\) ⇒ cos-1(sin θ) = \(\frac{\pi}{2}\) – θ

→ θ ∈ \(\left(-\frac{\pi}{2}, \frac{\pi}{2}\right)\) ⇒ cot-1(tan θ) = \(\frac{\pi}{2}\) – θ

→ θ ∈ (0, π) ⇒ tan-1(cot θ) = \(\frac{\pi}{2}\) – θ

→ θ ∈ [-\(\frac{\pi}{2}\), 0) ∪ (0, \(\frac{\pi}{2}\)] ⇒ sec-1(cosec θ) = \(\frac{\pi}{2}\) – θ

→ θ ∈ [0, \(\frac{\pi}{2}\)) ∪ (\(\frac{\pi}{2}\), π] ⇒ cosec-1(sec θ) = \(\frac{\pi}{2}\) – θ

→ 0 ≤ x ≤ 1 ⇒ sin-1(x) = cos-1\(\left(\sqrt{1-x^{2}}\right)\) and

→ If -1 ≤ x < 0 ⇒ sin-1(x) = -cos-1\(\left(\sqrt{1-x^{2}}\right)\)

→ -1 < x < 1 ⇒ sin-1(x) = tan-1\(\left(\frac{x}{\sqrt{1-x^{2}}}\right)\)

Inter 1st Year Maths 1A Inverse Trigonometric Functions Formulas

→ -1 ≤ x < 0 ⇒ cos-1(x) = π – sin-1\(\left(\sqrt{1-x^{2}}\right)\) = π + tan-1\(\left(\frac{\sqrt{1-x^{2}}}{x}\right)\)

→ 0 ≤ x ≤ 7 ⇒ cos-1(x) = sin-1\(\left(\sqrt{1-x^{2}}\right)\) = tan-1\(\left(\frac{\sqrt{1-x^{2}}}{x}\right)\)

→ x > 0 ⇒ tan-1(x) = sin-1\(\left(\frac{x}{\sqrt{1+x^{2}}}\right)\) = cos-1\(\left(\frac{1}{\sqrt{1+x^{2}}}\right)\)

→ tan-1(x) + tan-1(y) + tan-1(z) = tan-1\(\left[\frac{x+y+z-x y z}{1-x y-y z-z x}\right]\), ifx, y, z have the same sign and xy + yz + zx < 1.

→ 2 sin-1(x) = sin-12x\(\sqrt{1-x^{2}}\), if x ≤ \(\frac{1}{\sqrt{2}}\)
= π – sin-12x\(\sqrt{1-x^{2}}\), if x > \(\frac{1}{\sqrt{2}}\)

→ 2 cos-1(x) = cos-1(2x2 – 1), if x ≥ \(\frac{1}{\sqrt{2}}\)
= π – cos-1(1 – 2x2), if x < \(\frac{1}{\sqrt{2}}\)

→ 2 tan-1(x) = tan-1\(\left(\frac{2 x}{1-x^{2}}\right)\), if |x| < 1
= π – tan-1\(\left(\frac{2 x}{1-x^{2}}\right)\), if |x| ≥ 1

Inter 1st Year Maths 1A Inverse Trigonometric Functions Formulas

→ 2tan-1(x) = sin-1\(\left(\frac{2 x}{1+x^{2}}\right)\), ∀ x ∈ R
= cos-1\(\left(\frac{1-x^{2}}{1+x^{2}}\right)\), if x ≥ 0
= -cos-1\(\left(\frac{1-x^{2}}{1+x^{2}}\right)\), if x < 0
= tan-1\(\left(\frac{2 x}{1-x^{2}}\right)\), ∀ x ∈ R

→ 3 sin-1(x) = sin-1(3x – 4x3) for 0 ≤ x < \(\frac{1}{2}\)
3 cos-1(x) = cos-1(4x3 – 3x) for \(\frac{\sqrt{3}}{2}\) ≤ x < 1
3 tan-1(x) = tan-1\(\left\{\frac{3 x-x^{3}}{1-3 x^{2}}\right\}\) for 0 ≤ x < \(\frac{1}{\sqrt{3}}\)

→ If sin θ = x, we write θ = sin-1x.

→ sin(sin-1x) = x, sin-1(sin θ) = θ if ‘θ‘ ∈ \(\left[-\frac{\pi}{2}, \frac{\pi}{2}\right]\)

→ cos(cos-1x)=x, cos-1(cos θ) = θ if θ ∈ [0, n]

→ tan (tan-1x) = x, tan-1(tan θ) = θ if θ ∈ \(\left(-\frac{\pi}{2}, \frac{\pi}{2}\right)\)

→ That value of sin-1x lying between – \(\frac{\pi}{2}\) and\(\frac{\pi}{2}\) is called the principal value of sin-1x.

→ That value of cos-1x lying between 0 and π is called the principal value of cos-1x.

→ That value of tan-1x lying between – \(\frac{\pi}{2}\) and \(\frac{\pi}{2}\) is called the principal value of tan-1x.

→ If -1 ≤ x ≤ 1, then

  • sin-1(- x) = – sin-1x
  • cos-1(-x) = π – cos-1x

→ If x ∈ R , then

  • tan-1(-x) = -tan-1x
  • cot-1(-x) = π – cot-1x

→ If x ≤ -1 or x ≥ 1, then

  • cosec-1(-x) = -cosec-1x
  • sec-1(-x) = π – sec-1x

→ cosec-1x = sin-1\(\frac{1}{x}\) (if x ≠ 0)

→ sec-1x = cos-1\(\frac{1}{x}\) (if x ≠ 0)

→ cot-1x = tan-1\(\frac{1}{x}\) (if x > 0)
= π + tan-1\(\frac{1}{x}\) (if x < 0)

→ sin-1x + cos-1x = π/2 ,

→ tan-1x + cot-1x = π/2,

→ sec-1x + cosec-1x = π/2.

→ If sin-1x + sin-1y = π/2, then x2 + y2 = 1.

→ sin(cos-1x) = \(\sqrt{1-x^{2}}\), cos(sin-1x) = \(\sqrt{1-x^{2}}\)

→ sin-1 = cos-1\(\sqrt{1-x^{2}}\) for 0 ≤ x ≤ 1
= -cos-1\(\sqrt{1-x^{2}}\) for – 1 ≤ x ≤ 0