Tính S = 1 x 2 - 2 x 3 + 3 x 4 - 4 x 5 + 5 x 6 - 6 x 7 + ... - 1998 x 1999 + 1999 x 2000.
1. tính nhẩm :
53 x 201
=???
2. tìm x , biết :
a) 4 nhân x - 15 nhân 4 = 6 nhân 15 + x
b) (102 + 28 - 2 nhân x ) : 20 - 5 = 1
c) x nhân 1999 - x = 1999 + 1997 +1999
d) 105 - 5 nhân x = 150:15
e) ( x + 1 ) + ( x+2 ) + ( x + 3 ) + .... + ( x + 6 ) = 78
1 tìm x
a , ( x + 1 ) + ( x + 4 ) + ( x + 7 ) + ( x + 10) + ..........+ ( x + 28 ) = 155
b, ( x x 0,25 + 1999 ) x 2000 = ( 53 + 1999 ) x 2000
c, 71 + 65 x 4 = \(\frac{x+140}{x}\)x 260
a, x.2 + x.5 = 14 b, x.9 + x = 20
c, x: \(\dfrac{3}{2}\) + x.\(\dfrac{1}{3}\) = 1999 d,11.(x+2) = 5.x + 40
e, 11.(x-6) = 4.x + 11 f, (3.x - 4) : x + 10 = 12
g, (5.x + 7) : x + 20 = 26 h, x.1999 - x = 1999.1997 + 1999
***dấu chấm(.) = dấu nhân(x)***
a, x.2 + x .5 = 14 b, x.9 + x = 20
c, x: \(\dfrac{3}{2}\) + x. \(\dfrac{1}{3}\) = 1999 d, 11.(x+2) = 5.x + 40
e, 11.(x-6) = 4.x + 11 f, (3.x - 4) : x + 10 = 12
g, (5.x + 7) : x + 20 = 26 h, x.1999 - x = 1999.1997 + 1999
Bài 1:tìm x:
a) x+5*2-(32+16*3*6-15)= 0
b) (x*0,25+1999)*2000= (53+1999)*2000
c)x*2016=x:2016
d) (x+2)+(x+3)+.....................+ (x+100)= 5750-(x-1)
e) x+x:1/3:2/9+x:2/7= 252
g) 71+65*4=\(\frac{x+140}{x}\) + 260
h) x:0,1: 0,2: 0,3 :0,4 : 0,5 : 0,6 = 100000
tìm x : a. 6.25+x=(3.5+x)*1.5 b. x*(x-1999)-5*5=5*4
tìm x biết:
a) 5 *x - 1952 = 2500 - 1947
b) x *1999 - x =1999 *1997+ 1999
Tìm x:
a) (X x 0,25 + 1999) x 2000 = ( 53 + 1999 ) x 2000
b) 71 + 65 x 4 = \(\dfrac{x+140}{x}\) + 260