Pregunta
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Solve aor \( x \) in the follong equations. \( x^{x}=8 \)

Ask by Phillips Horton. in South Africa
Feb 24,2025

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The solution to the equation \( x^{x} = 8 \) is: \[ x = \exp(W(3 \ln 2)) \] or equivalently, \[ x = \frac{3 \ln 2}{W(3 \ln 2)} \] where \( W \) is the Lambert W function.

Solución

We wish to solve   xˣ = 8. A common method for equations where the variable appears both in the base and the exponent is to take logarithms. Here’s one way to proceed: 1. Write the equation as   xˣ = 8        (1) 2. Taking the natural logarithm of both sides gives   ln(xˣ) = ln(8). 3. Using the logarithm power rule (ln(aᵇ) = b·ln(a)), we have   x · ln(x) = ln(8). Since 8 = 2³, it follows that ln(8) = 3 ln2. Hence, we have   x · ln(x) = 3 ln2.      (2) 4. At this point it is useful to make the substitution   u = ln(x) ⟹ x = eᵘ. Then equation (2) becomes   eᵘ · u = 3 ln2. This equation is of the form   u · eᵘ = constant, which is exactly the type of equation solved by the Lambert W function. Recall that the Lambert W function, W(z), is defined as the function satisfying   W(z) e^(W(z)) = z. 5. Compare   u · eᵘ = 3 ln2    with  W(3 ln2) e^(W(3 ln2)) = 3 ln2. Thus, we can identify   u = W(3 ln2). 6. But u was defined as ln(x), so   ln(x) = W(3 ln2). Taking exponentials of both sides then gives   x = exp(W(3 ln2)). There is also an equivalent way to write the solution. Recall the property   exp(W(z)) = z/W(z). Thus, we may also write   x = (3 ln2) / W(3 ln2). This is the exact solution in closed form. To summarize, the solution for x in the equation xˣ = 8 is:   x = exp(W(3 ln2))     or equivalently,   x = (3 ln2) / W(3 ln2). Because the Lambert W function is not generally an elementary function, this answer is considered fully acceptable. Numerical evaluation will yield approximately x ≈ 2.39, which indeed satisfies xˣ ≈ 8.

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The Deep Dive

To solve \( x^x = 8 \), we can first express 8 as \( 2^3 \). This gives us the equation \( x^x = 2^3 \). Taking the logarithm of both sides, we get \( x \log(x) = 3 \log(2) \). This is a transcendental equation, which typically doesn't have a straightforward algebraic solution. However, we can use numerical methods or graphing to approximate the value of \( x \). By trial and error or utilizing software, we find that \( x \approx 2 \) is a close solution, since \( 2^2 = 4 \), and indeed \( 2^{2.5} = \sqrt{8} \) which is closer to 8, thus the precise answer lies between these values. If you dive deeper into numerical analysis or iteration methods, you could hone in on that value to get incredibly precise results!

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