Trigonometric Ratios & Identities

Expert Answer & Key Takeaways

Master trigonometric values, the CAST rule (quadrants), and fundamental identities to solve advanced math problems in SSC CGL.

Model 1: Ratios & Standard Values

  • sinθ=P/H\sin \theta = P/H, cosθ=B/H\cos \theta = B/H, tanθ=P/B\tan \theta = P/B
  • The Master Table: Memorize values for 0, 30, 45, 60, and 90.
  • Complementary: sin(90θ)=cosθ\sin(90-\theta) = \cos \theta, tan(90θ)=cotθ\tan(90-\theta) = \cot \theta.

Model 2: CAST Rule (Quadrants)

  • 1st (0-90): ALL Positive.
  • 2nd (90-180): Sin/Cosec Positive.
  • 3rd (180-270): Tan/Cot Positive.
  • 4th (270-360): Cos/Sec Positive.

Model 3: Fundamental Identities

  • sin2θ+cos2θ=1\sin^2\theta + \cos^2\theta = 1
  • 1+tan2θ=sec2θ1 + \tan^2\theta = \sec^2\theta (Implying sec2tan2=1\sec^2 - \tan^2 = 1)
  • 1+cot2θ=cosec2θ1 + \cot^2\theta = \text{cosec}^2\theta

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