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6 < x < 10 x

.x = 7 .4 < x < 8

:( ) ( )

x < 5 1.6 < x + 1 ⇔ x < 5 ×1.27 < x + 1

⇔ x < 6.32 < x + 1

. 5.32 < x < 6.32 . x > 5.32 x < 6.32

.x = 6

:( ) ()

6912 < 4n3 < 13500 ⇔ 1728 < n3 < 3375
⇔ 3 1728 < 3 n3 < 3 3375
⇔ 12 < n < 15

14 13

. 27

. :( ) ( )

z2 > 0 . ( ) ( )

x >y z <0 .

.( ) .xz < yz

:( ) ( )

. .d = 1 c = −2 b = 1 a = 1

d = 1 c = −2 b = 1 a = 0

.