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Given that tanθ=13\tan \theta = \frac{1}{3} and \sin \theta > 0, what is cosθ\cos \theta?

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Q. Given that tanθ=13\tan \theta = \frac{1}{3} and sinθ>0\sin \theta > 0, what is cosθ\cos \theta?
  1. Given Information: We are given that tanθ=13\tan \theta = \frac{1}{3} and \sin \theta > 0. We need to find cosθ\cos \theta. The tangent of an angle in a right triangle is the ratio of the opposite side to the adjacent side. Since tanθ=13\tan \theta = \frac{1}{3}, we can consider the opposite side to be 11 and the adjacent side to be 33 in a right triangle.
  2. Finding Opposite and Adjacent Sides: Using the Pythagorean theorem, we can find the hypotenuse of the triangle. The Pythagorean theorem states that in a right triangle, the square of the hypotenuse (the side opposite the right angle) is equal to the sum of the squares of the other two sides.\newlineLet's denote the hypotenuse as hh. Then we have:\newlineh2=opposite2+adjacent2h^2 = \text{opposite}^2 + \text{adjacent}^2\newlineh2=12+32h^2 = 1^2 + 3^2\newlineh2=1+9h^2 = 1 + 9\newlineh2=10h^2 = 10\newlineh=10h = \sqrt{10}
  3. Finding Hypotenuse: Now that we have the hypotenuse, we can find cosθ\cos \theta. The cosine of an angle in a right triangle is the ratio of the adjacent side to the hypotenuse.cosθ=adjacenthypotenuse\cos \theta = \frac{\text{adjacent}}{\text{hypotenuse}}cosθ=310\cos \theta = \frac{3}{\sqrt{10}}
  4. Finding Cosine: To rationalize the denominator, we multiply the numerator and the denominator by 10\sqrt{10}.
    cosθ=310×1010\cos \theta = \frac{3}{\sqrt{10}} \times \frac{\sqrt{10}}{\sqrt{10}}
    cosθ=31010\cos \theta = \frac{3\sqrt{10}}{10}

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