Discover Questions

Hello, can anyone tell me what crystals/ minerals these are? I notice the purple amethyst and rose Quartz? Not sure about the others. Thank? Physics: what is the purpose of using a dual mirror on a car? Math problem .Find the following quotient. 4-i/3+i Thanks? Let n>1 be a composite number. Prove that n does not divide (n - 1)! - 1(Hint: Factor n as n = ab with a,b < n. Argue by contradiction)? Hey I need some help
How do you know if a compound is predicted to be polar or non-polar?