When dealing with trigonometric functions, it is often necessary to simplify complex expressions into a single trigonometric function. This process can make equations easier to work with and provide insight into the behavior of the functions involved. In this article, we will explore various methods for writing a given expression as a single trigonometric function, along with examples to illustrate each technique.

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## Using Trigonometric Identities

One of the most common methods for simplifying trigonometric expressions is through the use of trigonometric identities. These identities allow us to rewrite complex expressions in terms of simpler trigonometric functions, such as sine, cosine, and tangent. Some of the fundamental identities include:

**Pythagorean identities:**These identities relate the squares of sine and cosine to each other. The most common form is:*sin*^{2}(x) + cos^{2}(x) = 1**Reciprocal identities:**These identities express one trigonometric function in terms of another by using reciprocals. For instance:*1/sin(x) = csc(x)***Quotient identities:**These identities express tangent and cotangent in terms of sine and cosine:*tan(x) = sin(x)/cos(x)*and*cot(x) = cos(x)/sin(x)***Even and odd function identities:**These identities exploit the symmetry properties of trigonometric functions. For example,*sin(-x) = -sin(x)*and*cos(-x) = cos(x)*

By utilizing these identities, we can manipulate trigonometric expressions to simplify them into a single function.

## Example:

Given the expression *(cos(x) – sin(x))/(cos(x) + sin(x))*, we can rewrite it using the quotient identity for tangent:

*(cos(x) – sin(x))/(cos(x) + sin(x)) = tan(x/2)*

Here, we have simplified the expression into a single trigonometric function using the quotient identity for tangent.

## Expressing in Terms of Sine and Cosine

Another common approach to simplifying trigonometric expressions is to express them in terms of sine and cosine. This can be achieved by using the Pythagorean identities and the reciprocal identities. By converting all trigonometric functions in an expression to either sine or cosine, we can often simplify the expression significantly.

## Example:

Consider the expression *tan(x) + cot(x)*. We can rewrite both tangent and cotangent in terms of sine and cosine:

*tan(x) + cot(x) = sin(x)/cos(x) + cos(x)/sin(x) = (sin ^{2}(x) + cos^{2}(x))/(sin(x)*cos(x)) = 1/(sin(x)*cos(x)) = csc(x)*sec(x)*

In this example, we have successfully expressed the given expression in terms of sine and cosine, resulting in a single trigonometric function.

## Using Double-Angle or Half-Angle Identities

Double-angle and half-angle identities can be powerful tools for simplifying trigonometric expressions. These identities allow us to express trigonometric functions of double or half angles in terms of simpler functions, which can lead to a more compact and comprehensible expression.

## Example (Double-Angle Identity):

Suppose we have the expression *2sin(x)cos(x)*. We can use the double-angle identity for sine to rewrite it as:

*2sin(x)cos(x) = sin(2x)*

By employing the double-angle identity, we have successfully written the given expression as a single trigonometric function.

## Combining Multiple Function Expressions

Sometimes, simplifying a trigonometric expression involves combining multiple function expressions into a single function. This could involve using addition and subtraction formulas, or multiplying and dividing different trigonometric functions to achieve a concise representation.

## Example:

Consider the expression *sin(x)cos(x) + tan(x)*. We can use the addition formula for sine to simplify it as follows:

*sin(x)cos(x) + tan(x) = sin(2x) + sin(x)/cos(x) = sin(2x) + sin ^{2}(x)/cos(x) = sin(2x) + (1 – cos^{2}(x))/cos(x) = sin(2x) + sec(x) – cos(x)*

In this example, we have combined multiple function expressions into a single trigonometric function.

## Conclusion

Writing a given trigonometric expression as a single function can greatly simplify mathematical manipulations and provide deeper insights into the behavior of the functions involved. By utilizing trigonometric identities, expressing in terms of sine and cosine, using double-angle or half-angle identities, and combining multiple function expressions, it is possible to transform complex expressions into more manageable forms. These techniques are essential tools for anyone working with trigonometric functions and can make mathematical analysis and problem-solving more efficient.

With a firm understanding of these methods, you can tackle complex trigonometric expressions with confidence, knowing that you have the tools to simplify them into a single trigonometric function.