Tìm x :
a ) 7 ( x-4 ) = 74 : 73
b ) 2x-105 : 21=15
c ) 15-5 ( x- 1 ) = 10
d ) ( x-12 ) :3 = 6
e ) 24 + 5 . x = 75 : 73
g ) x + 12.3=40
h ) 2x-138=23.32
i ) 231- ( x-6 ) = 1339 : 13
k ) 3x + 2x = 25
l ) 2x-42 : 8 = 12
m ) 12 ( x-1 ) :3=43- 23
n ) 128 : ( x-1 )2 =2
o ) x-34=2.32-1
ô ) 3+2x-1 = 24 - [ 42 -(22-1 ) ]
Viết gọn tổng sau :
A = 3+32+ 33 + 34+......+399+3100
So sanh :
A = 1=2+22+23+24+.....+249 và 250