Question

Difficulty: MediumTrigonometric Ratios and Identities

An acute angle θ\theta satisfies the equation sin(θ)=2425\sin(\theta) = \frac{24}{25}. What is the value of 1cos(θ)tan(θ)\frac{1}{\cos(\theta)} - \tan(\theta)?

  1. A
    34\frac{3}{4}
  2. 17\frac{1}{7}Answer
  3. C
    77
  4. D
    124\frac{1}{24}

Answer

The correct value of the expression is 17\frac{1}{7}.
The correct answer is 17\frac{1}{7}. Using the Pythagorean identity, we determine that cos(θ)=1sin2(θ)=725\cos(\theta) = \sqrt{1 - \sin^2(\theta)} = \frac{7}{25}. Using the definition of tangent, we find tan(θ)=sin(θ)cos(θ)=247\tan(\theta) = \frac{\sin(\theta)}{\cos(\theta)} = \frac{24}{7}. Substituting these values into the given expression yields 17/25247=257247=17\frac{1}{7/25} - \frac{24}{7} = \frac{25}{7} - \frac{24}{7} = \frac{1}{7}.

Step-by-Step Solution

1
Find the value of cos(θ)\cos(\theta) using the Pythagorean identity sin2(θ)+cos2(θ)=1\sin^2(\theta) + \cos^2(\theta) = 1.
cos(θ)=725\cos(\theta) = \frac{7}{25}
Since θ\theta is an acute angle, cos(θ)=1sin2(θ)=1(2425)2=49625=725\cos(\theta) = \sqrt{1 - \sin^2(\theta)} = \sqrt{1 - \left(\frac{24}{25}\right)^2} = \sqrt{\frac{49}{625}} = \frac{7}{25}.
2
Find the value of tan(θ)\tan(\theta) using the definition tan(θ)=sin(θ)cos(θ)\tan(\theta) = \frac{\sin(\theta)}{\cos(\theta)}.
tan(θ)=247\tan(\theta) = \frac{24}{7}
Substituting the known values gives tan(θ)=24/257/25=247\tan(\theta) = \frac{24/25}{7/25} = \frac{24}{7}.
3
Substitute the values of cos(θ)\cos(\theta) and tan(θ)\tan(\theta) into the expression 1cos(θ)tan(θ)\frac{1}{\cos(\theta)} - \tan(\theta) and simplify.
17\frac{1}{7}
The expression becomes 17/25247=257247=17\frac{1}{7/25} - \frac{24}{7} = \frac{25}{7} - \frac{24}{7} = \frac{1}{7}.

Key Concept

Pythagorean identity and trigonometric ratio definitions in a right triangle
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