ICSEClass XMathematicsTrigonometrical Identities04 Mark2023 Easy

QQuestion

Prove the following identity:

(sin2 θ − 1)(tan2 θ + 1) + 1 = 0

Exam-ready answer 04 Mark

Answer

Solving L.H.S. of the given equation :

⇒ (sin2 θ – 1)(tan2 θ + 1) + 1

⇒ (1 – cos2 θ – 1).sec2 θ + 1

⇒ -cos2 θ. sec2 θ + 1

\mathrm{LHS}=-\cos^2\theta\times\frac{1}{\cos^2\theta}+1

LHS = −1 + 1

LHS = 0

Since LHS = RHS, (sin2 θ − 1)(tan2 θ + 1) + 1 = 0 is proved.

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