Appearance
question:Let f be a real-valued function of one real variable. Suppose that f is three times differentiable and satisfies the equation f'''(x) = -f(x) for all x. If f(0) = f'(0) = 0 and f''(0) = 1, what are the values of the function f at the points x = π, x = -π, and x = π/2?
answer:To solve this problem, we need to find the general solution to the differential equation f'''(x) = -f(x). This is a linear homogeneous differential equation with constant coefficients, so we can start by assuming a solution of the form f(x) = e^(rx) for some constant r. Substituting this into the differential equation gives the characteristic equation r^3 + 1 = 0. The characteristic equation has three complex roots, which are r = -1, r = 1/2 + i√3/2, and r = 1/2 - i√3/2. The general solution to the differential equation is a linear combination of three solutions corresponding to these roots: f(x) = Ae^(-x) + Be^(x/2)cos(√3x/2) + Ce^(x/2)sin(√3x/2) is not a solution to the equation, however, a general solution can be created using those three roots. Using Euler's formula, we can express this solution as f(x) = A e^(-x) + B e^(x/2) e^(i√3x/2) + C e^(x/2) e^(-i√3x/2). With some rearrangement, the solution becomes f(x) = A e^(-x) + e^(x/2) (B e^(i√3x/2) + C e^(-i√3x/2)). This can be expressed using sine and cosine functions as: f(x) = A e^(-x) + e^(x/2) ((B+C) cos(√3x/2) + i(B-C)sin(√3x/2)). Since the problem statement says that f(x) is real-valued, the coefficients of the solution must be real, and the imaginary parts must cancel. So, B = C and the solution becomes f(x) = A e^(-x) + 2B e^(x/2) cos(√3x/2). Also, f'(x) = -A e^(-x) + B e^(x/2) (cos(√3x/2) - √3 sin(√3x/2)) and f''(x) = A e^(-x) + B e^(x/2) (-2 cos(√3x/2) - √3 sin(√3x/2)). Now, we can apply the initial conditions to find the values of A and B. The condition f(0) = 0 gives A + 2B = 0, and the condition f'(0) = 0 gives -A + B = 0. Solving these equations, we find that A = 0 and B = 0 cannot satisfy the initial condition f''(0) = 1, and we realize our general solution had an error and needed an adjustment. A correct general solution to f'''(x) = -f(x) is f(x) = c1e^(-x) + e^(x/2) (c2cos(√3x/2) + c3sin(√3x/2)) or, equivalently, using Euler's formula f(x) = A e^(-x) + B e^(x/2) e^(i√3x/2) + C e^(x/2) e^(-i√3x/2) which then when rearranged and simplified and noting that we need a real solution to a real-valued function we arrive at the following general solution with real coefficients: f(x) = c1 e^(-x) + e^(x/2) (c2 cos(√3x/2) + c3 sin(√3x/2)) for real coefficients c1, c2, and c3 or equivalently: f(x) = c1 e^(-x) + c2 e^(x/2) cos(√3x/2) + c3 e^(x/2) sin(√3x/2). Taking derivatives: f'(x) = -c1 e^(-x) + 1/2 c2 e^(x/2) cos(√3x/2) + 1/2 c3 e^(x/2) sin(√3x/2) - √3/2 c2 e^(x/2) sin(√3x/2) + √3/2 c3 e^(x/2) cos(√3x/2) and f''(x) = c1 e^(-x) + 1/4 c2 e^(x/2) cos(√3x/2) + 1/4 c3 e^(x/2) sin(√3x/2) - √3/4 c2 e^(x/
question:it is necessary to continue from there to be able to do the three questions.
answer:Continuing from where we left off, we can now use the initial conditions to find the values of c1, c2, and c3. From the condition f(0) = 0, we have c1 + c2 = 0. From the condition f'(0) = 0, we have -c1 + 1/2 c2 + √3/2 c3 = 0. From the condition f''(0) = 1, we have c1 + 1/4 c2 + √3/4 c3 = 1. Solving these equations simultaneously, we find that c1 = -1/3, c2 = 1/3, and c3 = 2√3/3. Now, we have the solution f(x) = (-1/3) e^(-x) + (1/3) e^(x/2) cos(√3x/2) + (2√3/3) e^(x/2) sin(√3x/2). To find the values of f at x = π, x = -π, and x = π/2, we can substitute these values into the solution. First, let's find the value of f at x = π: f(π) = (-1/3) e^(-π) + (1/3) e^(π/2) cos(√3π/2) + (2√3/3) e^(π/2) sin(√3π/2). Using the values of cos(√3π/2) = 0 and sin(√3π/2) = -1, we get f(π) = (-1/3) e^(-π) - (2√3/3) e^(π/2). Next, let's find the value of f at x = -π: f(-π) = (-1/3) e^(π) + (1/3) e^(-π/2) cos(√3(-π)/2) + (2√3/3) e^(-π/2) sin(√3(-π)/2). Using the values of cos(-√3π/2) = 0 and sin(-√3π/2) = 1, we get f(-π) = (-1/3) e^(π) + (2√3/3) e^(-π/2). Finally, let's find the value of f at x = π/2: f(π/2) = (-1/3) e^(-π/2) + (1/3) e^(π/4) cos(√3π/4) + (2√3/3) e^(π/4) sin(√3π/4). Using the values of cos(√3π/4) = -√2/2 and sin(√3π/4) = √2/2, we get f(π/2) = (-1/3) e^(-π/2) - (√6/6) e^(π/4) + (√6/3) e^(π/4). Simplifying further, we get f(π/2) = (-1/3) e^(-π/2) + (√6/6) e^(π/4).
question:For x = π and x = -π you simplified your final expressions so I am confused what the values are for x = π and x = -π.
answer:I will provide the simplified values for x = π and x = -π. For x = π: f(π) = (-1/3) e^(-π) - (2√3/3) e^(π/2) For x = -π: f(-π) = (-1/3) e^(π) + (2√3/3) e^(-π/2) Note that the values for e^(π), e^(-π), e^(π/2), and e^(-π/2) can be approximated, but I will provide the exact expressions as above. If you would like, I can also provide the approximate values for these expressions using the approximate values for e^(π), e^(-π), e^(π/2), and e^(-π/2).
question:I'm in my mid-40s, and I've been feeling stuck in my current job for several years. I feel like I'm just going through the motions and I'm not really making the kind of impact I want to in my career. I've been thinking about making a change, but I'm not sure where to start or what I want to do next. I'm worried that if I make the wrong choice, I'll be in an even worse situation than I am now. What should I do?
answer:Feeling stuck in a job can be demotivating and affect other areas of your life. It's great that you're taking the first step by acknowledging your dissatisfaction and wanting to make a change. To start, let's take a step back and try to identify what's causing your feelings of being stuck. Is it the work itself, the company culture, the industry, or something else? Reflecting on the root cause of your dissatisfaction can help you determine what you need to change. Rather than focusing on a specific job title or industry, think about what aspects of a career are important to you. What are your values, interests, and skills? What kind of work environment and culture do you thrive in? What kind of impact do you want to make in your career? It might be helpful to explore different areas and talk to people in various fields to gain insights and advice. Networking, attending industry events, or even taking on a side project can help you discover new opportunities and interests. It's natural to worry about making the wrong choice, but it's also important to remember that there's no one right path. Careers are often non-linear, and it's okay to take calculated risks and try new things. You can always learn from your experiences and adjust your path as needed. Consider giving yourself permission to explore and experiment, rather than feeling like you need to have it all figured out right now. What's the smallest step you can take today to start moving forward and exploring new possibilities?