SS E - The number of real solutions of the equation e** + 4e3* - 58e2* + 4X +1 = 0 is P 2a +
Detailed Explanation
1. Recognising Exponential–Polynomial Mix
The equation contains powers of . Because is always positive, we can safely set This converts the exponential equation to a pure polynomial:
2. Spotting Palindromic Structure
A polynomial is called palindromic when its coefficients read the same forward and backward. Dividing by (which is allowed since ) gives a symmetric expression in and :
Group the terms via the identity Define
Then the equation reduces to a quadratic in :
3. Solving the Quadratic in
Solve using the quadratic formula:
= \frac{-4 \pm \sqrt{256}}{2} = \frac{-4 \pm 16}{2}.$$ So $$u = 6 \quad\text{or}\quad u = -10.$$ ### 4. Feasibility Check Because $t>0$ we always have $t + \dfrac1t \ge 2$ (AM ≥ GM). Therefore * $u = 6$ is **allowed**. * $u = -10$ is **impossible**. ### 5. Returning to $t$ For $u = 6$: $$t + \frac1t = 6 \;\Longrightarrow\; t^{2} - 6t + 1 = 0.$$ Solve: $$t = 3 \pm 2\sqrt2.$$ Both roots are positive (\(3+2\sqrt2\approx5.828\); \(3-2\sqrt2\approx0.172\)). ### 6. Back to $x$ Since $t=e^{x}$, $$x_1 = \ln\!(3 + 2\sqrt2), \qquad x_2 = \ln\!(3 - 2\sqrt2).$$ Both are real. No other $t$ values exist, so **exactly two real $x$** satisfy the original equation.Simple Explanation (ELI5)
What is the question?
We are asked how many real‐number answers (roots) satisfy the funny looking equation made with the exponential function :
Idea in kid language
- Change the scary thing. Every time we see we put a new simpler letter (because is always positive).
- The giant equation becomes a simpler fourth‐degree (quartic) rule in .
- Notice the numbers in that new rule read the same forwards and backwards (palindromic). That special symmetry lets us shrink it to a second‐degree (quadratic) rule in .
- Solve the small quadratic, check which answers are possible (remember ), then turn them back to using .
- Count how many values come out.
When you do this carefully you get exactly two real answers.
Step-by-Step Solution
Step-by-Step Solution
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Substitution
gives -
Divide by (allowed since ):
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Use symmetry with :
Plug in:
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Solve the quadratic:
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Feasibility (): Reject . Keep .
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Recover from : Both values are positive.
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Return to using :
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Count roots: Two real values.
Answer: Number of real solutions
Examples
Example 1
Optics: Refractive index decays as e^{kx}. Sometimes equations for darkness points reduce to polynomial in e^{kx}.
Example 2
Electrical engineering: The transient response of an RLC circuit can lead to e^{st} terms. Symmetric characteristic equations allow similar tricks.
Example 3
Population dynamics: Logistic growth with harvesting can create equations where substituting e^{kx} simplifies analysis.
Visual Representation
References
- [1]I.A. Maron – Problems in Calculus of One Variable (polynomial-exponential substitution examples)
- [2]R.D. Sharma Objective Mathematics – Exponential equations section
- [3]Art of Problem Solving (AoPS) forum discussion: palindromic polynomials technique
- [4]Titu Andreescu & Dorin Andrica – An Introduction to Diophantine Equations (has t + 1/t trick examples)
- [5]NIST Digital Library of Mathematical Functions – Exponential and Logarithmic properties