Question: Plot is not produced

People im with error to show a plot, this is a wor for universty about mechanic materials, and i'm with this error... do not show the plot... before, i've a error because the variable x has values, and i've to unassign to have this.. without unassign, has error in domin of the plot... i dont know how to do this ! And ive to send the work today. 

Someone can help me about this?


Value of variables:
functions
plot algoritm...
plot algoritm

Thanks !

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