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Answers and comments
1 Holds for
x
positive, not for
x
0 or for
x
negative.
2
proposition
justification
n
b
is positivegive
bra
b
0 is positivealge
0
b
definition
3
proposition
justification
a
0
given
a
finition
0 is positivede
bra
0
a
is positivealge
a
0
definition
4
proposition
justification
a
0
given
finition
a
0
a
is positivede
bra
0 is positivealge
a
0
definition
Notice the difference between questions 3 and 4. Together they
show that 0
0. Question 4 is the
converse
of question
3. Question 3 is the
converse
of question 4.
a
a
5
proposition
justification
a
is positive
0
a
qn 2
a
is positive
a
0
qns 2, 3 and 4
a
0or
a
is positiveor
a
is
trichotomy
positive
a
0or0
a
or
a
0
from above
6
proposition
justification
b
a
given
a
(
b
) is positivede
finition
b
bra
a
is positivealge
a
b
definition
