2N+2N+1 10 B, 3N+3+2N+3+3N+1+2N+2 6HD
Bài 2: Chứng minh rằng:
a,
8.2
n
+
2
n+
1
10
b,
3
n
+
3
+
2
n
+
3
+
3
n
+
1
+
2
n
+
2
6
HD:
a, Ta có:
8.2n
+2n
+
1
=8.2n
+2 .2 2 8 2n
=n
(
+ =)
10.2 10n
b, Ta có:
VT
=
3 .27 3 .3 2 .8 2 .4
n
+
n
+
n
+
n
=
3 .30 2 .12 6
n
+
n