how to do iteration starting with a known number

hello i need to do an iteration process to obtain (pws) i have several variables that pws depend on and i need to know how to solve the problem here is a screenshot for the problem

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>> and all elements in the question are present like pts,tts,l and theta

thank you

[dpb]

What have you done so far?

[mohamed]

ok so far i got the first value but i dont know how to tell matlab to substitute with the new value of pws again