Given that [tex]\tan (t) = \frac{5}{12}[/tex], and [tex]0 \ \textless \ t \ \textless \ \frac{\pi}{2}[/tex], complete the steps to find [tex]\cos (t)[/tex].

Which identity would be best to start with?



Answer :

To find [tex]\(\cos(t)\)[/tex] given [tex]\(\tan(t) = \frac{5}{12}\)[/tex] and [tex]\(0 < t < \frac{\pi}{2}\)[/tex], we can use trigonometric identities.

### Step-by-Step Solution:

1. Understand the Pythagorean Identity:
We know that [tex]\(\tan(t) = \frac{\sin(t)}{\cos(t)}\)[/tex]. Given [tex]\(\tan(t) = \frac{5}{12}\)[/tex], we can set up the relationship:
[tex]\[ \sin(t) = 5k \quad \text{and} \quad \cos(t) = 12k \][/tex]
for some constant [tex]\(k\)[/tex].

2. Use the Pythagorean Identity:
The Pythagorean identity for sine and cosine is:
[tex]\[ \sin^2(t) + \cos^2(t) = 1 \][/tex]
Substitute [tex]\(\sin(t) = 5k\)[/tex] and [tex]\(\cos(t) = 12k\)[/tex]:
[tex]\[ (5k)^2 + (12k)^2 = 1 \][/tex]

3. Simplify the Equation:
[tex]\[ 25k^2 + 144k^2 = 1 \][/tex]
Combine the like terms:
[tex]\[ 169k^2 = 1 \][/tex]

4. Solve for [tex]\(k\)[/tex]:
[tex]\[ k^2 = \frac{1}{169} \][/tex]
[tex]\[ k = \sqrt{\frac{1}{169}} \][/tex]
[tex]\[ k = \frac{1}{\sqrt{169}} \][/tex]
[tex]\[ k = \frac{1}{13} \][/tex]

5. Find [tex]\(\sin(t)\)[/tex] and [tex]\(\cos(t)\)[/tex]:
[tex]\[ \sin(t) = 5k = 5 \left(\frac{1}{13}\right) = \frac{5}{13} \][/tex]
[tex]\[ \cos(t) = 12k = 12 \left(\frac{1}{13}\right) = \frac{12}{13} \][/tex]

Thus, [tex]\(\cos(t) = \frac{12}{13}\)[/tex], and the corresponding values of [tex]\(\sin(t)\)[/tex] and [tex]\(\cos(t)\)[/tex] are:

[tex]\[ \sin(t) \approx 0.38461538461538464 \][/tex]
and
[tex]\[ \cos(t) \approx 0.9230769230769231 \][/tex]