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How to prove the following using the Order properties of Real Numbers?
1.If a,b element of Real number and a<b,then a<a+b/2<b.
2.If a<b and c<d,then ad+bc < ac+bd.

Sagot :

Chayieegaloviz
set examples. 
1. a<b , a<a+b/2<b 
   = a<a+b/2                                              = a+b/2<b 
   = 2a < 2a + b                                         = 2a +b <b
   = 2a -2a <b                                            = 2a<0
   = 0 < b                                             
which doesnt prove anything. so lets set examples. 
say for example a= -5 , b= -4 
-5<-5+-2<-4
-5<-7<-4  ,   -5 is not less than -7 it is more than -7 
hence, <b , a<a+b/2<b is not always true. 

2. a<b and c<d then ad+bc < ac+bd 
   = ad-ac<bd-bc
   = a(d-c)<b(d-c) 
   = a < b which is stated in the above statement.