Answer:
1. I agree with you.= <u><em>I don't agree with you/ I disagree with you.</em></u>
2. I think you're right.= <u><em>I don't think you're right/ I think you're wrong</em></u>.
3. I told her to go home.= <u><em>I didn't tell her to go home/ I told her not to go home.</em></u>
4. "Is John coming?" "I hope so."= <u><em>"Isn't John coming?" "I hope not."</em></u>
5. I knew everybody at the party.= <u><em>I didn't know anybody at the party</em></u>.
6. I've already done my homework.= <u><em>I've not done my homework</em></u>.
7. You must get a visa.= <u><em>You mustn't get a visa.</em></u>
8. My sister likes hip-hop, too.= <u><em>My sister doesn't like hip-hop, too</em></u>.
Explanation:
Changing positive sentences to negative sentences require the change in the condition of the helping verbs along with adding the adverb "not". And these words can be used in their contracted forms. Moreover, a negative condition means changing the positivity of the sentence into the exact opposite.
Thus, the given sentences can be changed into the negative form as follows-
<em>1. I don't agree with you/ I disagree with you.
</em>
<em>2. I don't think you're right/ I think you're wrong.
</em>
<em>3. I didn't tell her to go home/ I told her not to go home.
</em>
<em>4. "Isn't John coming?" "I hope not."
</em>
<em>5. I didn't know anybody at the party.
</em>
<em>6. I've not done my homework.
</em>
<em>7. You mustn't get a visa.
</em>
<em>8. My sister doesn't like hip-hop, too.</em>
