A= 5/13+ -5/7+ -20/41+ 8/13+ -21/41
A= (5/13+ 8/13) + [-20/41 + (-21/41)] + -5/7
A= 1 + (-1) + (-5/7)
A= [1 + (-1)] + (-5/7)
A= 0 + (-5/7)
A= -5/7
B= -4/12+ 18/45+ 6/-9+ 24/30
B= (-4/12+ 24/30) + [18/45 + (-6/9)]
B= 7/15 + -4/15
B=3/15
C= 1/3+ -3/4+ 3/5+ -1/36+ 1/15+ -2/9
C= (3/5+ 1/15) + [-3/4+(-1/36)] + [1/3 + (-2/9)]
C= 2/3 + (-7/9) + 1/9
C=2/3 + [(-7/9) + 1/9]
C=2/3 + -2/3
C=0
D= (-5/6 +8/15)+(19/-56 + 7/15)+3/-18
D= -5/6 +8/15+19/-56 + 7/15+3/-18
D= (-5/6 +3/-18) + (8/15 + 7/15) + (-19/56)
D= -1 + 1 + (-19/56)
D= 0 +(-19/56)
D=(-19/56)
TIM X:
I x-1/4 I= 3/2+ 7/6+ 1/-3
⇔ I x-1/4 I= 7/3
Trường hợp 1 Trường hợp 2
x-1/4 = -7/3 x-1/4 = 7/3
x = -7/3 + (-1/4) x = 7/3 + 1/4
x= -31/12 x = 31/12