I see the image contains a set of mathematical questions. I'll transcribe and explain the contents:

Q1:

(a) What do the following terms mean to you?

• Arbitrary constant
• Boundary value problems
• Nonlinear operator

(b) Classify equation:
$u = xyt \quad \text{and} \quad \frac{\partial^2 u}{\partial t^2} + c_1f_1 + c_2f_2 = c_1 Lf_1 + c_2 Lf_2$

Q2:

(a) Solve the differential equation:
$x y^{\prime\prime\prime} + y = 3x^3$
With initial conditions:
$y(0) = 1, \quad y'(0) = 0, \quad y''(0) = -3, \quad y^{\prime\prime\prime}(0) = 0$

(b) Solve:
$y^{(4)} - 9y = 0, \quad y(0) = 1$

Q3:

(a) Solve:
$z = \left(\frac{\partial z^2}{\partial x}\right) \left(\frac{\partial^2 z}{\partial y^2}\right)$

(b) By using Laplace transform or separation of variables, solve:
$\frac{\partial u}{\partial t} = 3 \frac{\partial u}{\partial x}, \quad \text{with} \quad u(x,0) = 4e^{-2x}$

Would you like me to solve specific parts of these questions or explain any concepts in detail?

Here are 5 potential follow-up questions to help guide you:

1. What is the difference between linear and nonlinear operators?
2. How can boundary value problems differ from initial value problems?
3. What is the general method to classify partial differential equations (PDEs)?
4. Can you explain how to approach higher-order differential equations like $y^{(4)} - 9y = 0$?
5. How do Laplace transforms simplify the solution of partial differential equations?

Tip: When solving differential equations, it's useful to first check if the equation can be simplified by methods such as Laplace transforms, factoring, or substitution before applying general solution techniques.