
Yefim S. answered 04/21/21
Math Tutor with Experience
g'(x) = 12e12xsinh(8x) + 8e12xcosh(8x) = 0; e12x ≠ 0, so 3sinh(8x) + 2cosh(8x) = 0
tan(8x) = - 2/3; (e8x - e-8x)/(e8x + e-8x) = - 2/3; 3e8x - 3e-8x = - 2e8x - 2e-8x; 5e8x = e-8x; e-16x = 5;
x = - ln5/16 = - 0.10059