Tìm x
a) [(3.x-3/5):0,75].1/2/3+1/3=1
b) 1999.2001-1/1998+1999.2000 . 7/5.x=1
c) 11,13 + 13,15 + 15,17 + ... +31,33 = 5.x+11,13
d) (x+1,75):0,12=1+2-3+4-5+6- ... +118-119+120
e) (2/11.13 + 2/13.15 + ... + 2/19.21 ) . 462 - [2,04 : ( x + 1,05 ) ] : 0,12 = 11,5