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. x ( x < a, x > a, x = a).
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M(a,b) :
a > 0, b > 0 (I),
a < 0, b > 0 (II),
a < 0, b < 0 (III),
a >0, b < 0 (IV) .
, (a > 0, b > 0), (a < 0, b > 0; a < 0, b < 0; a >0, b < 0).
(a > 0, b > 0, c > 0). .
( ).
( N). ( N+1).
. . 4.1.
. 4.1.
( ) , .
( ) , , .