Final answer:
The sentence 'Bill Gates co-founded Microsoft' is in active voice. The passive voice equivalent is 'Microsoft was co-founded by Bill Gates'. The voice changes depending on whether the emphasis is on the doer or the action itself.
Step-by-step explanation:
The sentence 'Bill Gates co-founded Microsoft' is already in the active voice. In the active voice, the subject of the sentence (Bill Gates) performs the action (co-founded Microsoft).
The corresponding passive voice would be 'Microsoft was co-founded by Bill Gates.' In the passive voice, the subject of the sentence (Microsoft) is acted upon by the verb (was co-founded).
This change of voice involves changing the form of the verb and sometimes introducing a preposition (in this case 'by'). The object of the active voice sentence (Microsoft) becomes the subject in the passive voice sentence.
Use of active or passive voice depends on what a writer or speaker wants to emphasize. The active voice emphasizes the actor, while the passive voice emphasizes the action or the recipient of the action.
Learn more about Active and Passive Voice