Question

What does this symbol mean:
<=>
in math?

Answer 1

if and only if. it means the implication goes both directions. for example
\[x+2=7\iff x=5\]

Answer 2

compare to
\[x=4 \implies x^2=16\]

Answer 3

because the implication does not go the other way. if
\[x^2=16\] we do not know that
\[x=4\] only that
\[x=4\text{ or } x=-4\]

Answer 4

what does:
==>
mean? You told me what it implies, but what does it mean?

Answer 5

..... it means that:

(this) -> (that)
(this) implies (that)
If (this) then (that)