Plz explain as much as possible.

(a) (Direct proof) Show that for all integers n greater than 2 , the number 1+2++n is composite. (Recall that a positive integer is composite if it has at least one divisor other than 1 and itself.) (b) (Proof by contradiction) Prove by contradiction that if x+x>0, then x must be positive. (c) (Induction) Prove by induction that (141)(191)(1n21)=2nn+1