Question

1, cho a<b.Hãy so sánh : 5(7-2a)-8 và 5(7-2b)-8

Answer 1

\(a< b\)

\(\Leftrightarrow-2a>-2b\)

\(\Leftrightarrow7-2a>7-2b\)

\(\Leftrightarrow5\left(7-2a\right)>5\left(7-2b\right)\)

\(\Leftrightarrow5\left(7-2a\right)-8>5\left(7-2b\right)-8\)

Answer 2

\(35-10a-8=27-10a\)

\(35-10b-8=27-10b\)

a<b ==> 27-10a > 27-10b 

==> 5(7-2a) > 5(7-2b)-8