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Mathematics20236 marksNumericalIntegrals

Solve the following.

Evaluate: ∫ (3e²ˣ - 2eˣ)/(e²ˣ + 2eˣ - 8) dx

Evaluate: $\int \frac{3e^{2x} - 2e^x}{e^{2x} + 2e^x - 8}\,dx$

Answer

Answer

Integral: $\int \left((3*exp(2x) - 2*exp(x))/(exp(2x) + 2*exp(x) - 8)\right) dx$

Put $e^x = t$, so $e^x\,dx = dt$ and $dx = \frac{dt}{t}$. $\int \frac{3e^{2x} - 2e^x}{e^{2x}+2e^x-8}dx = \int \frac{3t-2}{t^2+2t-8}dt = \int \frac{3t-2}{(t+4)(t-2)}dt$ Partial fractions: $\frac{3t-2}{(t+4)(t-2)} = \frac{A}{t+4} + \frac{B}{t-2}$, giving $A = \frac{7}{3}$, $B = \frac{2}{3}$. $= \frac{7}{3}\log|t+4| + \frac{2}{3}\log|t-2| + C$ Hence the result is $\frac{7}{3}\log(e^x+4) + \frac{2}{3}\log|e^x-2| + C$.

Final answer: $\frac{7}{3}\log(e^x+4) + \frac{2}{3}\log|e^x-2| + C$