Trigonometric Identities and Laws

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Questions and Answers

Which of the following is a Pythagorean identity?

  • tan(x) = sin(x)/cos(x)
  • 1 + tan²(x) = sec²(x) (correct)
  • sin(x) = 1/csc(x)
  • cot(x) = cos(x)/sin(x)

The area of a triangle can be calculated using the formula Area = (1/2)ab * cos(C).

False (B)

What is the double angle formula for sine?

sin(2x) = 2sin(x)cos(x)

The law of sines states that a/sin(A) = b/sin(B) = c/sin(C). Fill in the blank. The ratio of side 'b' over sin(B) is equal to _____ over sin(A).

<p>a</p> Signup and view all the answers

Match the trigonometric identities with their corresponding formulas:

<p>Pythagorean Identity = sin²(x) + cos²(x) = 1 Quotient Identity = tan(x) = sin(x)/cos(x) Reciprocal Identity = csc(x) = 1/sin(x) Double Angle Formula = sin(2x) = 2sin(x)cos(x)</p> Signup and view all the answers

Flashcards

Reciprocal Identities

Relates the sine, cosine, and tangent of an angle to the cosecant, secant, and cotangent of the same angle.

Pythagorean Identities

States that the square of the sine of an angle plus the square of the cosine of the same angle equals 1.

Law of Cosines

Used to solve triangles where you know two sides and the included angle or two angles and one side.

Law of Sines

Relates the sides and angles of a triangle. It states that the ratio of a side to the sine of its opposite angle is constant.

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Sum and Difference Formulas

Expresses the sine, cosine, and tangent of a sum or difference of two angles in terms of the trigonometric functions of the individual angles.

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Study Notes

Trigonometric Identities

  • Reciprocal Identities: These relate trigonometric functions to each other.

  • sin(x) = 1/csc(x), cos(x) = 1/sec(x), tan(x) = 1/cot(x)

  • csc(x) = 1/sin(x), sec(x) = 1/cos(x), cot(x) = 1/tan(x)

  • Pythagorean Identities: Based on the Pythagorean theorem, these connect sine and cosine.

  • sin²(x) + cos²(x) = 1

  • 1 + tan²(x) = sec²(x)

  • 1 + cot²(x) = csc²(x)

  • Quotient Identities: These define tangent and cotangent in terms of sine and cosine.

  • tan(x) = sin(x)/cos(x)

  • cot(x) = cos(x)/sin(x)

Law of Cosines & Law of Sines

  • Law of Cosines: Used to find sides and angles in triangles.
  • c² = a² + b² - 2ab * cos(C)
  • Law of Sines: Another useful tool for finding unknown sides and angles.
  • a/sin(A) = b/sin(B) = c/sin(C)

Area of a Triangle (Trigonometric Form)

  • Calculating the area of a triangle using trigonometric functions.
  • Area = (1/2)ab * sin(C)

Sum and Difference Formulas

  • Sine:
  • sin(A ± B) = sin(A)cos(B) ± cos(A)sin(B)
  • Cosine:
  • cos(A ± B) = cos(A)cos(B) ∓ sin(A)sin(B)
  • Tangent:
  • tan(A ± B) = [tan(A) ± tan(B)] / [1 ∓ tan(A)tan(B)]

Double Angle Formulas

  • Sine:
  • sin(2x) = 2sin(x)cos(x)
  • Cosine:
  • cos(2x) = cos²(x) - sin²(x) = 2cos²(x) - 1 = 1 - 2sin²(x)
  • Tangent:
  • tan(2x) = 2tan(x) / [1 - tan²(x)]

Half-Angle Formulas

  • Sine:
  • sin(x/2) = ±√[(1 - cos(x))/2]
  • Cosine:
  • cos(x/2) = ±√[(1 + cos(x))/2]
  • Tangent:
  • tan(x/2) = ±√[(1 - cos(x))/(1 + cos(x))]
  • tan(x/2) = sin(x) / [1 + cos(x)] or [1 - cos(x)] / sin(x)

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