Answer:
x ∈ {-0.465, 1.014}
Step-by-step explanation:
The equation can be cast in the form f(x) = 0, and solved easily using a graphing calculator. That shows x ≈ -0.465 and x ≈ 1.014. The same calculator can iterate the roots to full calculator precision.
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The equation can be made a quadratic by the substitution ...
z = e^(2x)
Then we have ...
[tex]2\cosh(2x)-\sinh(2x)=4\\\\2\cdot\dfrac{e^{2x}+e^{-2x}}{2}-\dfrac{e^{2x}-e^{-2x}}{2}-4=0\qquad\text{use exponential identities}\\\\2z+2z^{-1}-z+z^{-1}-8=0\qquad\text{multiply by 2, substitute z}\\\\z^2 -8z+3=0\qquad\text{multiply by z}\\\\z=\dfrac{8\pm\sqrt{(-8)^2-4(1)(3)}}{2(1)}=4\pm\sqrt{13}\\\\x=\dfrac{\ln(z)}{2}=\dfrac{\ln(4\pm\sqrt{13})}{2}\approx\{-0465133,1.014439\}[/tex]
