Kenneth S. answered 12/04/16
Tutor
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Expert Help in Algebra/Trig/(Pre)calculus to Guarantee Success in 2018
Your question is non-specific. In a case like this, I suggest that you set aside some study time, and review CAREFULLY all of your textbook material in this area. I also suggest that you participate in a study group. I also suggest that you need to obtain remediation from your teacher or, if that is not feasible, you should have an in-person tutor.
The internet could be helpful, depending on the quality of inquiries you may make; consider Googling geometric proofs, angles in a parallelogram, etc. Have you ever tried Kahn Academy?