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a. Vì 125 125x127 – 127 127x125 = 1001x125x127 – 1001x127x125 = 0
nên : (1+3+5+...+2005)(125 125x127 – 127 127x125) = 0
b.
19 , 8 : 0 , 2 x 44 , 44 x 2 x 13 , 2 : 0 , 25 3 , 3 x 88 , 88 : 0 , 5 x 6 , 6 : 0 , 125 x 5 = 19 , 8 x 5 x 88 , 88 x 13 , 2 x 4 3 , 3 x 88 , 88 x 2 x 6 , 6 x 8 x 5 = 19 , 8 x 5 x 88 , 88 x 13 , 2 x 4 3 , 3 x 88 , 88 x 13 , 2 x 4 x 2 x 5 = 19 , 8 3 , 3 x 2 = 3
( 1+3+5+7+…+2003+2005) x (125 125 x 127 – 127 127 x 125)
= ( 1+3+5+7+…+2003+2005) x (125 x 1001 x 127 – 127 x 1001x 125)
= ( 1+3+5+7+…+2003+2005) x 0 = 0
Vì 125 125x127 – 127 127x125 = 1001x125x127 – 1001x127x125 = 0
nên : (1+3+5+...+2005)(125 125x127 – 127 127x125) = 0
( 1 + 3 + 5 + 7 +... + 2003 + 2005 ) x ( 125125 x 127 - 127127 x 125 )
= ( 1 + 3 + 5 + 7 + ... + 2003 + 2005 ) x ( 125 x 1001 x 127 - 127 x 1001 x 125 )
= ( 1 + 3 + 5 + 7 + ... + 2003 + 2005 ) x 0
= 0
~ Thiên Mã ~
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a, 2006 x 2004 - \(\frac{2}{1995}\) + 2004 x 2005 = 8038043,999
b, 2006 x 125 + \(\frac{1000}{126}\) x 2006 - 1006 = 265664,6349
c, A = 1991 x 1999
=> A = ( 1995 - 4 ) x ( 1995 + 4 )
A = 1995 x ( 1995 + 4 ) - 4 x ( 1995 + 4 )
A = 1995 x 1995 + 1995 x 4 - ( 4 x 1995 + 4 x 4 )
A = 1995 x 1995 - 4 x 4
mà B = 1995 x 1995
Vậy A < B
d, Gọi giá trị biểu thức là C
C = \(\frac{1}{3}+\frac{1}{6}+\frac{1}{12}+\frac{1}{24}+\frac{1}{48}+\frac{1}{96}\)
C x 2 = \(\frac{2}{3}+\frac{2}{6}+\frac{2}{12}+\frac{2}{24}+\frac{2}{48}+\frac{2}{96}\)
C x 2 = \(\frac{2}{3}+\frac{1}{3}+\frac{1}{6}+\frac{1}{12}+\frac{1}{24}+\frac{1}{48}\)
Vậy C x 2 - C = \(\left(\frac{2}{3}+\frac{1}{3}+\frac{1}{6}+\frac{1}{12}+\frac{1}{24}+\frac{1}{48}\right)-\left(\frac{1}{3}+\frac{1}{6}+\frac{1}{12}+\frac{1}{24}+\frac{1}{48}+\frac{1}{96}\right)\)
C = \(\frac{2}{3}-\frac{1}{96}\) ( vì phân số nào có ở số bị trừ cũng có ở số trừ thì trừ hết rồi nên không còn )
C = \(\frac{21}{32}\)
A=1991x1999=(1995-4)1999=1995x1999-4x1999
B=1995x1995=1995x(1999-4)=1995x1999-1995x4>1995x1999-4x1999=A
vậy A<B
bài 1 : 0
bài 2 : ( 8.78 + 1.25 ) x y= 26.3
10.03 x y = 26.3
y = 26.3 : 10.03
y = 2630/1003
bài 3 :diện tích HTG ABC là :
12 x 18 : 2 = 108 ( cm2 )
quên rùi
Trả lời
a)(1+3+5+7+...+2005).(125125.127-127127.125)
=(1+3+5+7+...+2005).0
=0
b)A=1001.1999 < 1995.1995
Học tốt !
1) a Tính nhanh
(1 + 3 + 5 + 7 + ... + 2005) . (125125 . 127 - 127127.125)
= (1 + 3 + 5 + 7 + ... + 2005) . (125.1001 .127 = 127.1001.125)
= (1 + 3 + 5 + 7 + ... + 2005) . 0
= 0
b) A = 1991 . 1999
= (1995 - 4) . (1995 + 4)
= 1995. 1995 + 1995 . 4 - 4 . 1995 - 4.4
= 1995.1995 - 16 < 1995.1995 = B
=> A < B
Chúc bạn học tốt !!