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Math

Math Snap

PROBLEM

6. Prove the Trig Identities.
a. cosθ×tanθ=sinθ\cos \theta \times \tan \theta=\sin \theta

STEP 1

1. We assume the basic trigonometric identities are known: tanθ=sinθcosθ\tan \theta = \frac{\sin \theta}{\cos \theta}.
2. We assume the domain of θ\theta is such that cosθ0\cos \theta \neq 0.

STEP 2

1. Express tanθ\tan \theta in terms of sinθ\sin \theta and cosθ\cos \theta.
2. Substitute the expression for tanθ\tan \theta into the left-hand side of the identity.
3. Simplify the expression to show it equals the right-hand side.

STEP 3

Start by expressing tanθ\tan \theta in terms of sinθ\sin \theta and cosθ\cos \theta:
tanθ=sinθcosθ\tan \theta = \frac{\sin \theta}{\cos \theta}

STEP 4

Substitute the expression for tanθ\tan \theta into the left-hand side of the identity cosθ×tanθ\cos \theta \times \tan \theta:
cosθ×tanθ=cosθ×sinθcosθ\cos \theta \times \tan \theta = \cos \theta \times \frac{\sin \theta}{\cos \theta}

SOLUTION

Simplify the expression by canceling cosθ\cos \theta in the numerator and the denominator:
cosθ×sinθcosθ=sinθ\cos \theta \times \frac{\sin \theta}{\cos \theta} = \sin \theta The identity is proven:
cosθ×tanθ=sinθ\cos \theta \times \tan \theta = \sin \theta

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