Degrees or Radians modelling?

I was doing question 9 from the 2022 Edexcel A-Level paper 2 (https://www.mathsgenie.co.uk/alevel/a-level-pure2-2022.pdf) and I was wondering why you would use degrees instead of radians I thought you always use radians in calculus? (I used differentiation to get one of my values)

I was doing question 9 from the 2022 Edexcel A-Level paper 2 (https://www.mathsgenie.co.uk/alevel/a-level-pure2-2022.pdf) and I was wondering why you would use degrees instead of radians I thought you always use radians in calculus? (I used differentiation to get one of my values)

You don't need to use calculus. Maximum value of R sin(kx + a) is R (because the maximum value of sin is 1). Similarly for cos.
If you differentiated without converting to radians, you probably got a derivative 180/pi bigger than it should be. But if you were just looking for where the derivative is zero this wouldn't actually matter in terms of getting the right answer. I'd expect it to lose you method marks though.

You don't need to use calculus. Maximum value of R sin(kx + a) is R (because the maximum value of sin is 1). Similarly for cos.
If you differentiated without converting to radians, you probably got a derivative 180/pi bigger than it should be. But if you were just looking for where the derivative is zero this wouldn't actually matter in terms of getting the right answer. I'd expect it to lose you method marks though.

also this was my working

is it wrong because once you use radians to find the value of A and you plug it back into the original equation in degrees you would change the calculator to degrees?