Difficulty: Easy
Correct Answer: 5/√3
Explanation:
Introduction / Context:
This problem tests your knowledge of exact trigonometric ratios for special angles, particularly 30° and 60°. It asks you to use those values to evaluate an expression involving secant and tangent, and then simplify it into a compact surd form commonly used in exam answers.
Given Data / Assumptions:
Concept / Approach:
We recall that sec θ = 1 / cos θ and tan θ = sin θ / cos θ. For 30° and 60°, the cosine and sine values are well known: cos 30° = √3/2, sin 30° = 1/2, sin 60° = √3/2 and cos 60° = 1/2. Using these, we compute sec 30° and tan 60° exactly, then add them and simplify the result into a single fraction with a rational numerator and a surd denominator.
Step-by-Step Solution:
cos 30° = √3/2, so sec 30° = 1 / cos 30° = 1 / (√3/2) = 2/√3.
For 60°, sin 60° = √3/2 and cos 60° = 1/2.
So tan 60° = sin 60° / cos 60° = (√3/2) / (1/2) = √3.
Now compute sec 30° + tan 60° = 2/√3 + √3.
Write √3 as 3/√3 (since 3/√3 = √3).
Then 2/√3 + √3 = 2/√3 + 3/√3 = 5/√3.
Verification / Alternative check:
We can approximate numerically to confirm. cos 30° ≈ 0.866 so sec 30° ≈ 1.155. tan 60° ≈ 1.732. Their sum is about 2.887. Now 5/√3 ≈ 5 / 1.732 ≈ 2.887 as well. The close numerical match confirms that the simplified expression 5/√3 is correct.
Why Other Options Are Wrong:
(√6 + 1)/√3 and (√3 + 2)/√3 have different numerators and do not evaluate to approximately 2.887. (1 + √3)/2 is around 1.366, which is far from the true value. The option 2√3 is approximately 3.464, again not matching the computed sum. Only 5/√3 agrees with the exact algebraic simplification and the numerical check.
Common Pitfalls:
Students sometimes confuse sec 30° with sec 60° or mistakenly use tan 30° instead of tan 60°. Another frequent error is to skip the step of rewriting √3 as 3/√3, which can make it harder to combine terms. Carefully recall the exact values for special angles and handle surds step by step to avoid mistakes.
Final Answer:
Thus, sec 30° + tan 60° has the exact value 5/√3.
Discussion & Comments