A, 3N+2−2N+2+3N−2 10N B, 3N+2−2N+4+3N+2 30NHD
Bài 1: Chứng minh rằng:
a,
3
n
+
2
−
2
n
+
2
+
3
n
−
2 10
n
b,
3
n
+
2
−
2
n
+
4
+
3
n
+
2 30
n
HD :
a, Ta có:
VT=3 .9 2 .4 3n
−n
+ − =n
2n
3 9 1n
( )
+ −2 .8 2 .2n
−
1
−n
−
1
=
3 .10
n
−
2 .10 10
n−
1
b, Ta có:
VT=3 .9 2 .16 3n
−n
+ + =n
2n
3 9 1n
( )
+ −2 16 1n
(
− =)
3 .10 2 .15 30n
−n