I don't know if - You say this when you're clueless, but your teacher says it'

You say this when you're clueless, but your teacher says it's not valid. You're a dumb student who doesn't know anything.

I don't know if I should do my math homework. My teacher said that's not a valid answer.

I don't know if I should write the essay. My teacher said that's not a valid answer.

I don't know if I should take the test. My teacher said that's not a valid answer.