How do I know if a sentence is in the active or passive voice?

Remember: If the subject is performing the action, then the sentence is in active voice. If the subject is simply receiving the action, then the sentence is in passive voice. Shift the object of the action into the beginning of the sentence.  

Example:

You did not pay your bill.

cassius, casca, and their allies plant false documents to manipulate brutus to join their cause to remove caesar. after doing so, they visit brutus at night in his home to persuade him of their views. there they plan caesar's death. brutus is troubled but refuses to confide in his devoted wife, portia. on 15 march, caesar's wife, calpurnia, urges him not to go to the senate. she has had visionary dreams and fears the portents of the overnight storms.

identify the non-linear equation.   identify the non-linear equation.