Tìm X :
(X x 81+ 2 x 81 - 3530) x 21 = 714
X x 81+ 2 x 81 - 3530 = 714 : 21
X x 81+ 2 x 81 - 3530 = 34
X x 81 + 2 x 81 = 34 + 3530
81 x (X + 2) = 3564
X + 2 = 3564 : 81
X + 2 = 44
X = 44 - 2
X = 42
( X x 81 + 2 x 81 - 3530) x 21 = 714
<=> 81 x X + 162 - 3530 = 714 : 21
<=> 81 x X - 3368 = 34
<=> 81 x X = 3402
<=> X = 3402 : 81
<=> X = 42