Question

prove that a+d > b+c​

Answer 1

Answer:

If b and d are positive, you just need to multiply both sides by bd . If they are both negative that also works. If b and d have opposite signs then you can multiply both sides by −bd . But then you get −abd/b>−bcd/d , i.e. −ad>−bc which is equivalent to ad<bc . In other words the inequality reverses if bd<0 .