Casio FX-991EX and FX-300ES

[Pekis]

Hello,
I tried it with Casio fx 5800p, which has Solver but prohibiting integral or d/dx within it: combined with a very small secant method program, I introduced this formula in a separate subroutine (under the form f(Z)->Y, to solve for Z):

integral(1/X, 101325, 200000) * 8.314 / 40644 - integral (1/X^2, 373.15, Z)->Y

Result: 393.57804, after 18 iterations starting from Z=2, in approx. 35 sec.