If \(\tan \theta=\frac{12}{5}\), then \(\cos \theta=\)

The tangent function is one of the primary trigonometric functions and is abbreviated as \(\tan\). It relates the angles of a right-angled triangle to the ratio of the triangle's opposite side over its adjacent side. More formally, \(\tan(\theta) = \frac{\text{opposite}}{\text{adjacent}}\).

In the unit circle, where all triangles have a hypotenuse of length 1, the tangent function represents the length of the segment tangent to the circle from the point where the line through the origin makes an angle \(\theta\) with the positive x-axis.

Special Values and Properties

Tangent has some unique properties. For example, it is periodic with a period of \(\pi\) radians, meaning \(\tan(\theta) = \tan(\theta + n\pi)\) for all integers \(n\). Additionally, it has asymptotes, points where the function heads towards infinity, at \(\theta = \frac{\pi}{2} + n\pi\). This is due to the cosine function, which is in the denominator of the tangent ratio, approaching zero at these points.

The cosine function, denoted as \(\cos\), is another fundamental trigonometric function that represents the ratio of the adjacent side to the hypotenuse of a right-angled triangle. Simply put, \(\cos(\theta) = \frac{\text{adjacent}}{\text{hypotenuse}}\).

Unit Circle Interpretation

In trigonometry, using the unit circle is a powerful way to understand the function. On this circle, the cosine function gives the x-coordinate of the point formed by the intersection of the terminal side of the angle \(\theta\) and the circle.

Regarding the shape of the cosine graph, it is a wave which starts at 1 (when \(\theta = 0\)) and oscillates between the values 1 and -1 for every period of \(2\pi\) radians. The cosine function is an even function, meaning it is symmetric with respect to the y-axis, which tells us \(\cos(\theta) = \cos(-\theta)\).

Trigonometric identities are equations that relate the trigonometric functions to one another. They are true for all values of the involved angles and are incredibly useful for simplifying expressions and solving equations that involve trigonometric functions.

Pythagorean Identity

The Pythagorean identity, as shown in the original exercise, states that \(\sin^2(\theta) + \cos^2(\theta) = 1\). Since the tangent function is \(\tan(\theta) = \frac{\sin(\theta)}{\cos(\theta)}\), we can manipulate the Pythagorean identity to involve tangent as well: \(\tan^2(\theta) + 1 = \frac{1}{\cos^2(\theta)}\), a crucial step in solving the provided exercise.

Understanding and being able to derive these relationships between sinusoidal functions can considerably streamline the process of solving trigonometric problems.

Solving trigonometric equations involves finding the values of the angles that satisfy the equation. The steps usually involve using trigonometric identities, algebraic manipulation, and sometimes the inverse trigonometric functions.

Methodology

Generally, one starts by isolating the trigonometric function, as was done in the steps of the provided solution. It's important to consider the function’s domain and range since functions like cosine and sine can have multiple solutions within a single period. Furthermore, the quadrant of the angle can affect the sign of the solution, as with the cosine function, which can take on both positive and negative values.

Always verify whether additional solutions exist by exploring the fundamental period of the trigonometric function involved. Lastly, it’s crucial to simplify results where possible and state them clearly, as ambiguous solutions can lead to confusion.