1998^2-1997(1998+1)
=1998^2-(1998-1)(1998+1)
=1998^2-(1998^2-1)
=1998^2-1998^2+1
=1
1998^2-1997(1998+1)
=1998^2-(1998-1)(1998+1)
=1998^2-(1998^2-1)
=1998^2-1998^2+1
=1
Tính nhanh
138^2-38^2
99^2+99×2+1
85^2+85×30+15^2
(10^2+8^2+6^2+4^2+2^2)-(9^2+7^2+5^2+3^2+1)
1998^2-1997×(1998+1)
862 - 142=?
19982 - 1997. (1998+1)=?
1988^2-1997(1998+1)
\(\dfrac{x+1}{1998}\)+ \(\dfrac{x+2}{1997}\)=\(\dfrac{x+3}{1996}\)+\(\dfrac{x+4}{1995}\)
1997^2 -1996*1998..... Giup mình với
Tính nhanh:
a) 642 + 382 + 128 . 36 ; b) 76 . 56 - (353 + 2) . (353 - 2) ; c) 19972 - 1996 . 1998
a,x-10/1994+x-8/1996+x-6/1998+x-4/2000+x-2/2002=x-2002/2+x-2000/4+x-1998/6+x-1996/8+x-1994/10
b,x-1991/9+x-1993/7+x-1995/5+x-1997/3+x-1999/1=x-9/1991+x-7/1993+x-5/1995+x-3/1997+x-1/1999
c,x-1/13-2x-13/15=3x-15/27-4x-27/29
so sánh 2 số avàb biết
a=6+5^2+5^3+.....+5^1997+5^1998
b=(5^999*(5^1000+2)-10*5^998-1)/4
A = x2000 - 2000x1999 + 2000x1998 - 2000x1997 + ... - 2000x2 + 2000x + 727
Tính A tại x = 1999