To evaluate the definite integral \(\int_{0}^{\pi / 2} e^{\sin (x)} \cos (x) \, dx\), we can use a substitution method. Let \(u = \sin(x)\). Then, \(du = \cos(x) \, dx\). The limits of integration will change accordingly: when \(x = 0\), \(u = \sin(0) = 0\); and when \(x = \pi/2\), \(u = \sin(\pi/2) = 1\). The integral then simplifies to \(\int_{0}^{1} e^u \, du\), which is straightforward to evaluate.
Step 1: Substitution
To evaluate the definite integral \(\int_{0}^{\pi / 2} e^{\sin (x)} \cos (x) \, dx\), we use the substitution \(u = \sin(x)\). Then, \(du = \cos(x) \, dx\).
Step 2: Change of Limits
The limits of integration change accordingly:
When \(x = 0\), \(u = \sin(0) = 0\).
When \(x = \pi/2\), \(u = \sin(\pi/2) = 1\).
Step 3: Simplified Integral
The integral simplifies to:
\[
\int_{0}^{1} e^u \, du
\]
Step 4: Evaluate the Integral
The integral of \(e^u\) with respect to \(u\) is \(e^u\). Evaluating this from 0 to 1, we get:
\[
\left[ e^u \right]_{0}^{1} = e^1 - e^0 = e - 1
\]
Step 5: Numerical Value
The numerical value of \(e - 1\) is approximately 1.7183.