The solution to the differential equation is given by: \[ y = \left[ \left( \frac{C_2 + C_3}{C_1} \right) e^{C_4} \right] e^x = A e^x, \] where \( A = \left( \frac{C_2 + C_3}{C_1} \right) e^{C_4} \) is a consolidated constant.
The order of the differential equation is determined by the number of independent arbitrary constants, which in this case is 1.
Let \( f : \mathbb{R} \to \mathbb{R} \) be a twice differentiable function such that \( f(x + y) = f(x) f(y) \) for all \( x, y \in \mathbb{R} \). If \( f'(0) = 4a \) and \( f \) satisfies \( f''(x) - 3a f'(x) - f(x) = 0 \), where \( a > 0 \), then the area of the region R = {(x, y) | 0 \(\leq\) y \(\leq\) f(ax), 0 \(\leq\) x \(\leq\) 2\ is :