Răspuns :
x = 7/12 + ( - 5/18)
x = 7/12 - 5/18
x = (3×7 - 2×5)/36
x = (21 - 10)/36
x = 11/36
y = - 13/24 - ( - 7/18)
y = - 13/24 + 7/18
y = - 13×3/72 + 7×4/72
y = -39/72 + 28/72
y = - 11/72
11/72 este opusul nr ( - 11/72)
11/36 + 11/72 = 2×11/72 + 11/72 = 22/72 + 11/72 = 33/72 = 11/24 (suma)
x = 7/12 - 5/18
x = (3×7 - 2×5)/36
x = (21 - 10)/36
x = 11/36
y = - 13/24 - ( - 7/18)
y = - 13/24 + 7/18
y = - 13×3/72 + 7×4/72
y = -39/72 + 28/72
y = - 11/72
11/72 este opusul nr ( - 11/72)
11/36 + 11/72 = 2×11/72 + 11/72 = 22/72 + 11/72 = 33/72 = 11/24 (suma)
x = 7/12+(-5/18)
y = -13/24-(-7/18)
S = x+(-y)
S = x-y
S = 7/12+(-5/18) - (-13/24-(-7/18))
S = 7/12-5/18 + 13/24 - 7/18
S = 7/12 + 13/24 - 5/18-7/18
S = (7×2)/24+13/24 -12/18
S = 14/24+13/24-12/18
S =27/24 - 12/18
S = 27/24 - 2/3
S = 27/24 - (2×8)/24
S = 27/24 - 16/24
S = (27-16)/24
S = 11/24
y = -13/24-(-7/18)
S = x+(-y)
S = x-y
S = 7/12+(-5/18) - (-13/24-(-7/18))
S = 7/12-5/18 + 13/24 - 7/18
S = 7/12 + 13/24 - 5/18-7/18
S = (7×2)/24+13/24 -12/18
S = 14/24+13/24-12/18
S =27/24 - 12/18
S = 27/24 - 2/3
S = 27/24 - (2×8)/24
S = 27/24 - 16/24
S = (27-16)/24
S = 11/24