Just imagine that as a lecturer, I am presenting a topic, and I have some related slides.
Where the words are in bold face, I am in doubts. Would you please correct me?
"... as you can see, in [on or at] this slide, our calculation formula is written [or has been written/was written]. This formula is only for [or is for only] the situation that mentioned [has been mentioned/is mentioned/was mentioned] in [or without in] our last session. Also, the formula is explained [was explained/has been...] in your book on [at] page 100 ..."
Additionally, would you please explain briefly about the reasons of your correction?
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.
Thanks so much. I have another question as well. A person asked me about my BSc thesis' language (I got my BSc 4 yrs ago), and I said, "it is written in Persian". Now, my friend says that you should say, "it was written in Persian", and the way that you said is completely wrong.
So, would you please tell me that was my sentence completely wrong?
No, it's not wrong. You could use either form. Yes, the writing that you did was in the past. But the paper itself is written in Persian.