Bài 14:
a)3^4.5^4-(15^2+1)(15x^2-1)
=(3.5)^4-(15^4-1^2)
=15^4-15^4+1
=1
b)
=( 85^2- 15^2)+(75^2-25^2)+(65^2-35^2)+(55^2-45^2)
=(85-15)(85+15)+(75-25)(75+25)+(65-35)(65+35)+(55-45)(55+45)
=70.100+50.100+30.100+10.100
=16000
c)
Đặt A=1^2-2^2+.....-2016^2
=>-A=2^2-1^2+4^2-3^2+6^2-5^2+2016^2-2015^2
-A=(2-1)(2+1)+(4-3)(4+3)(6-5)(6+5)....+(2016-2015)(2016+2015)
-A=3=7+11+..+4031
=((4031-3):4+1):2.(3.4031)
A=-2033136
d)
=(5^2-1)(5^2+1)(5^4+1)(5^8+1)(5^16+1):2
=(5^4-1)(5^4+1)(5^8+1)(5^16+1):2
=(5^8+1)(5^8-1)(5^16+1):2
=(5^16-1)(5^16+1):2
=(5^23-1):2
e)
=3/4.8/9.15/16.24/25.....99/100
=1.3/2.2 . 2.4/3.3 . 3.5/4.4 . 4.6/5.5......9.11/10.10
=1.2.3.4...9/2.3.4.5.10 . 3.4.5.6...11/2.3.4.5.10
=1/10.11/2
=11/20
