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Geometry and Trigonometry / Right triangles and trigonometry Difficulty: Easy

Triangle $A B C$ is similar to triangle $D E F$ , where angle $A$ corresponds to angle $D$ , and angles $C$ and $F$ are right angles. If $\cos B = \frac{1}{22}$ , what is the value of $\cos E$ ?

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Explanation

Choice A is correct. The cosine of an acute angle in a right triangle is defined as the ratio of the length of the leg adjacent to that angle to the length of the hypotenuse. It's given that angle $C$ is a right angle in triangle $A B C$ and that angle F is a right angle in triangle $D E F$ . Therefore, $\cos B$ is equal to the ratio of the length of side $B C$ to the length of side $A B$ , and $\cos E$ is equal to the ratio of the length of side $E F$ to the length of side $D E$ . It’s also given that triangle $A B C$ is similar to triangle $D E F$ , where angle $A$ corresponds to angle $D$ . Since similar triangles have proportional side lengths, $\frac{B C}{A B} = \frac{E F}{D E}$ . Therefore, the value of $\cos B$ is equal to the value of $\cos E$ . Since $\cos B = \frac{1}{22}$ , the value of $\cos E$ is $\frac{1}{22}$ .

Choice B is incorrect and may result from conceptual errors.

Choice C is incorrect and may result from conceptual errors.

Choice D is incorrect and may result from conceptual errors.