Question bank / Right triangles and trigonometry

Math · Geometry and TrigonometryMedium

In a right triangle, the hypotenuse has length 2626, and the sine of one of the acute angles is 513\frac{5}{13}. What is the area of the triangle?

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Answer: 120

If sin⁡θ=513\sin \theta = \frac{5}{13}, the leg opposite θ\theta has length 513(26)=10\frac{5}{13}(26) = 10. By the Pythagorean theorem, the other leg has length 262−102=576=24\sqrt{26^2 - 10^2} = \sqrt{576} = 24. The area is 12(10)(24)=120\frac{1}{2}(10)(24) = 120.

Using leg lengths 55 and 1212 gives an area of 3030, but this triangle's hypotenuse is 2626, so its sides are twice as long and its area is 44 times as large.

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