Question

If a 11 years ago

Answer 1

My attempt: a<b --> a-b <0
\(c\leq d\rightarrow c-d \leq 0\)
add them to get a +c -(b+d)\(\leq \) 0
so that a+ c \(\leq \) b+d
but the question is about < , not \(\leq \)

Answer 2

@kirbykirby

Answer 3

I got it.