ACT Math · Right-triangle trigonometry

In a right triangle, one acute angle measures 35°, and the leg adjacent to that angle has length 10. Which value is closest to the length…

35°10x
In a right triangle, one acute angle measures 35°, and the leg adjacent to that angle has length 10. Which value is closest to the length of the opposite leg?

Answer and explanation

Answer: J: 7.0

The opposite and adjacent legs are connected by the tangent: tan⁡35∘=opposite10\tan 35^\circ=\frac{\text{opposite}}{10}, so the opposite leg is 10tan⁡35∘≈10(0.700)=7.010\tan35^\circ\approx10(0.700)=7.0, choice J. Choice G (12.212.2) is 10cos⁡35∘\frac{10}{\cos35^\circ}, the hypotenuse, not a leg. Choice F (5.75.7) is 10sin⁡35∘10\sin35^\circ, which would be correct only if 10 were the hypotenuse. Choice H (8.28.2) is 10cos⁡35∘10\cos35^\circ, another ratio that uses the wrong side. Match the ratio to the sides given: opposite over adjacent is the tangent.

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