david.017

Hey, I'm currently struggle with these two proofs, if anyone can help me I would be very thankful. 1. prove that one of the roots of x^3+ax^3 +bx + c = 0 is the negative of another if and only if c=ab. 2. Prove that if the diagonals of a quadrilateral divide it into four triangles of equal area, then the quadrilateral is a parallelogram.

well it wasn't assignment work, its just that I read it in a textbook a while ago but couldn't really figure it out. Thanks for your input though

Hey, I read this question a while ago and was wondering if anyone could come up with proof for this question. Let a1,a2,a3,a4, and a5 be any distinct positive integers. Show that there exists at least one subset of 3 of these integers whose sum is divisble by 3. (Use the fact that every integer can be writtein in the form of 3k, 3k+1, 3k+2, where k isa int). Thanks, this question has been bothering me for quite some time now