Question

Find the real part, the imaginary part, and the absolute value of $$ \cosh (i x) $$

Short answer

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Step-by-step solution

Understand the Hyperbolic Cosine Function

The hyperbolic cosine function is defined as

Key concepts

Hyperbolic Cosine

The hyperbolic cosine, denoted as \(\text{cosh}(x)\), is a mathematical function similar to the regular cosine but it relates to hyperbolic geometry. Unlike regular cosine, which uses a circle, hyperbolic cosine is based on a hyperbola. The formula for hyperbolic cosine is:
\[ \text{cosh}(x) = \frac{e^x + e^{-x}}{2} \]
This function is incredibly useful in various fields like calculus, physics, and engineering.
When we deal with the hyperbolic cosine of an imaginary number, like \(\text{cosh}(ix)\), we can use Euler's formula to help us. Euler's formula states:
\[ e^{ix} = \text{cos}(x) + i \text{sin}(x) \]
This formula connects complex numbers and trigonometry. Using Euler's formula, we can find:
\[ \text{cosh}(ix) = \frac{e^{ix} + e^{-ix}}{2} \]
Applying Euler's formula inside the hyperbolic cosine equation will allow us to separate the real and imaginary parts.

Imaginary Numbers

Imaginary numbers are a type of complex number which are multiples of the imaginary unit, denoted as \(i\), where \(i\) is defined as the square root of -1. In mathematical terms:
\[ i = \frac{1}{\text{sqrt}(-1)} \]
Imaginary numbers provide an essential tool for solving equations that require the square root of a negative number.
When dealing with \(\text{cosh}(ix)\), note that \(ix\) is an imaginary number.
Using the properties of imaginary numbers helps to simplify and understand complex expressions. For example, think of \(e^{ix}\) and \(e^{-ix}\) from Euler's formula. Substituting \(e^{ix}\) and \(e^{-ix}\) into the \(\text{cosh}(ix)\) equation, we get:
\[ e^{ix} = \text{cos}(x) + i \text{sin}(x) \]
\[ e^{-ix} = \text{cos}(x) - i \text{sin}(x) \]
These substitutions will elucidate the real and imaginary parts in our hyperbolic function solution.

Absolute Value Calculation

The absolute value, also known as the modulus, of a complex number \(a + bi\) is calculated as:
\[ \text{abs}(a + bi) = \text{sqrt}(a^2 + b^2) \]
This formula allows us to find the distance of a complex number from the origin in the complex plane.
For \(\text{cosh}(ix)\), once we have the real and imaginary parts, the absolute value becomes straightforward to calculate.
Suppose we determined that \(\text{cosh}(ix) = \text{cos}(x)\), meaning our function has no imaginary part (i.e., \(b = 0\)), our absolute value would be:
\[ \text{abs}(\text{cos}(x)) = \text{sqrt}(\text{cos}^2(x)) \]
Because the square root of a square is the absolute value itself, it simplifies to:
\[ \text{abs}(\text{cos}(x)) = \text{cos}(x) \]
Remember, the real part is \(\text{cos}(x)\) and it determines our absolute value straightforwardly.