Tính nhanh nếu có thể
A) 1/3.-7/5+-7/3.1/5
B)15/4.4/5+17/13.169/221
C) 1/56+1/72+1/90+1/110+1/132+1/56
D)4/21+4/77+4/165+4/285+4/437+4/621
Tính nhanh nếu có thể A) 1/3.-7/5+-7/3.1/5 B)15/4.4/5+17/13.169/221 C) 1/56+1/72+1/90+1/110+1/132+1/56 D)4/21+4/77+4/165+4/285+4/437+4/621
By Savannah
Đáp án:
A) 1/3.-7/5+-7/3.1/5= -7/15 + 7/15 = 0
B)15/4.4/5+17/13.169/221 = 3 + 1 = 4
C) 1/56+1/72+1/90+1/110+1/132+1/56 = 2/63 + 2/99 + 47/1848
= 4/77 + 47/1848 = 13/168
D)4/21+4/77+4/165+4/285+4/437+4/621 = 8/33 + 8/209 + 8/513
= 16/57 + 8/513 = 8/27
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