Tìm x:
a, (11/12 + 11/12. 23 + 11/23. 24 + ….+ 11/89. 100)+ x= 5/3
b, (2/11. 13 + 2/13. 15 + ….+ 2/19. 21)- x + 4+ 221/231 = 7/3
Tìm số nguyên n để biểu thức sau có giá trị nguyên:
4/n-1 + 6/n-1 – 3/n-1
Tìm x:
a, (11/12 + 11/12. 23 + 11/23. 24 + ….+ 11/89. 100)+ x= 5/3
b, (2/11. 13 + 2/13. 15 + ….+ 2/19. 21)- x + 4+ 221/231 = 7/3
Tìm số nguyên n để biểu thức sau có giá trị nguyên:
4/n-1 + 6/n-1 – 3/n-1
Đáp án:
a.
(1112+1112×23+1123×34+...+1189×100)+x=23(1112+1112×23+1123×34+…+1189×100)+x=23
(1112+112−123+123−134+...+189−1100)+x=23(1112+112−123+123−134+…+189−1100)+x=23
(1112+112−1100)+x=23(1112+112−1100)+x=23
(1212−1100)+x=23(1212−1100)+x=23
(1−1100)+x=23(1−1100)+x=23
(100−1100)+x=23(100−1100)+x=23
99100+x=2399100+x=23
x=23−99100x=23−99100
x=200−297300x=200−297300
x=−97300x=−97300
b.
(211×13+213×15+...+219×21)−x+221231=43(211×13+213×15+…+219×21)−x+221231=43
(111−113+113−115+...+119−121)+221231−x=43(111−113+113−115+…+119−121)+221231−x=43
(111−121)+221231−x=43(111−121)+221231−x=43
(21−11231)+221231−x=43(21−11231)+221231−x=43
10231+221231−x=4310231+221231−x=43
231231−x=43231231−x=43
1−x=431−x=43
x=1−43x=1−43
x=3−43x=3−43
x=−13
n=11