How can i select pdf while asking questions here

(not sure if you needed help with inserting an actual pdf or a picture) so you go to input your question like you did, but before you submit, click on the question bar where you were typing. Then it will show you your question and other little things to the left hand corner on the bottom. Click on the paper clip and then you can insert a picture. (if you already knew that and just wanted to insert an actual pdf file I don't think that you can do that but you can take a screenshot of it and then just insert that

Iwould say they are complementary because that’s the division of a 90 degree angle and it’s split between the middle of them