tính nhanh
1x2 + 2x3 + 3x4 + 4x5 +5x6 + 6x7 + 7x8 + 8x9 + 9x10
Tính tổng:
A= 1x2+2x3+3x4+4x5+5x6+6x7+7x8+8x9+9x10+10x11+...+99x100
1/1x2 + 1/2x3 + 1/3x4 + ... 1/99 x 100
Tìm x biết 1/1x2 + 1/2x3 + 1/3x4 + ... + 1/X(X+1) = 99/100
A=1x2+2x3+3x4+...+99x100
B=1^2+2^2+...+99^2+100^2
C=5+55+555+...+555...5(có 100 chữ số 5)
(1-1/2)(1-1/3)(1-1/4)….(1-1/2002).x=1-1/1x2-1/2x3-1/3x4-...1/2002x2003
1313/1212 : x = 1/1x2+1/2x3+1/3x4+1/4x5+1/5
Tìm y :
\(\frac{9}{10}x100-\left(\frac{5}{2}:\left(y+\frac{206}{100}\right)\right):\frac{1}{2}=89\)
bài 1 tính
a, 24 x 66 - 24 + 36 x 24
b, 29 x 173 - 29 x 72 -29
c, 1+5+10+15+...+55+60
d, 1x2+2x3+3x4 +...+18x19+19x20
bài 2 tìm x
a,106- ( x+ 7) =9
b, 2 x ( x+ 4) + 5 =65
c, (16x x -32) x 45=0
d, x+4 x x = 100 : 5