Solving ODE in Mathematica

[jennwatkins16 (Jen Watkins)]

I am a student pursuing an engineering degree and am taking an introductory course on nuclear engineering. One of our “computational exercises” is

I don’t understand the output I’m getting. I used y and x instead of N and t since I had read somewhere that N shouldn’t be used. The output I’m looking for is e^-lambda(t) or in this case e^-lamda x. Can someone help me figure out where I’m going wrong?

Thanks

[iamorozov1 (Ivan Morozov)]

You defined \lambda y as one symbol, not as \lambda \cdot y:

DSolve[y'[x] == - lambda y[x], y[x], x]
DSolve[y'[x] == - lambday[x], y[x], x]

I.M.

[jennwatkins16 (Jen Watkins)]

Thank you!