Thực hiện phép tính một cách hợp lý:
A= -1/90-1/72-1/56-1/42-1/30-1/20-1/12-1/6-1/2
Thực hiện phép tính sau một cách hợp lí:
-1/90 - 1/72 - 1/56 - 1/42 - 1/30 - 1/20 -1/12 - 1/6 - 1/2
Ta có: -1/90 - 1/72 - 1/56 - 1/42 - 1/30 - 1/20 - 1/12 - 1/6 - 1/2
= (-1).(1/90 + 1/72 + 1/56 + 1/42 + 1/30 + 1/20 + 1/12 + 1/6 + 1/2)
= (-1).(1/2 + 1/6 + 1/12 + 1/20 + 1/30 + 1/42 + 1/56 + 1/72 + 1/90)
= (-1).(1/1 - 1/2 + 1/2 - 1/3 + ... + 1/9 - 1/10)
= (-1).(1 - 1/10)
= (-1).(9/10)
= -9/10
Thực hiện phép tính một cách hợp lý: \(-\frac{1}{90}-\frac{1}{72}-\frac{1}{56}-\frac{1}{42}-\frac{1}{30}-\frac{1}{20}-\frac{1}{12}-\frac{1}{6}-\frac{1}{2}\)
= - ( 1/2 +1/6+1/12+1/20+ 1/30+ 1/42+ 1/56+ 1/72+ 1/90)
= - ( 1 - 1/2 + 1/2 -1/3 +1/3 -1/4 +1/4 - 1/5 +1/5 -1/6 +1/6 -1/7 +1/7 -1/8 +1/8 -1/9 +1/9 -1/10)
= - ( 1- 1/10 )
= -9/10
\(-\frac{1}{90}-\frac{1}{72}-\frac{1}{56}-\frac{1}{42}-\frac{1}{30}-\frac{1}{20}-\frac{1}{12}-\frac{1}{6}-\frac{1}{2}\)
\(=\left(-\frac{1}{90}\right)+\left(-\frac{1}{72}\right)+\left(-\frac{1}{56}\right)+......+\left(-\frac{1}{2}\right)\)
\(=\left(-1\right).\left(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+........+\frac{1}{9.10}\right)\)
\(=\left(-1\right).\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...........+\frac{1}{9}-\frac{1}{10}\right)\)
\(=\left(-1\right).\left(1-\frac{1}{90}\right)=\frac{\left(-1\right).89}{90}=-\frac{89}{90}\)
nha
thực hiện phép tính 1 cách hợp lí
8/9 - 1/72 -1/56 -1/42 - 1/30 - 1/20 - 1/12 - 1/6 - 1/2
Bài 1: Thực hiện phép tính bằng cách hợp lý b)\(\frac{9}{8}-\frac{1}{2}-\frac{1}{6}-\frac{1}{12}-\frac{1}{20}-\frac{1}{30}-\frac{1}{42}-\frac{1}{56}-\frac{1}{72}\)
\(\frac{9}{8}-\frac{1}{2}-\frac{1}{6}-\frac{1}{12}-...-\frac{1}{72}=\frac{9}{8}-\left(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+...+\frac{1}{72}\right)\)
\(=\frac{9}{8}-\left(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{8.9}\right)\)
\(=\frac{9}{8}-\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{8}-\frac{1}{9}\right)\)
\(=\frac{9}{8}-\left(1-\frac{1}{9}\right)=\frac{9}{8}-\frac{8}{9}=\frac{17}{72}\)
Thực hiện phép tính
B=(-1/2)+(-1/6)+(-1/12)+(-1/20)+(-1/30)+(-1/42)+(-1/56)+(-1/72)+(-1/90)
A=1/90-1/72-1/56-1/42-1/30-1/20-1/12-1/6-1/2
Tính bằng cách hợp lý
bn vào link này nhé:https://olm.vn/hoi-dap/detail/49652619071.html
A = \(\frac{1}{90}-\frac{1}{72}-\frac{1}{56}-...-\frac{1}{6}-\frac{1}{2}\)
= \(\frac{1}{90}-\left(\frac{1}{72}+\frac{1}{56}+...+\frac{1}{6}+\frac{1}{2}\right)\)
= \(\frac{1}{90}-\left(\frac{1}{2}+\frac{1}{6}+...+\frac{1}{56}+\frac{1}{72}\right)\)
= \(\frac{1}{90}-\left(\frac{1}{1.2}+\frac{1}{2.3}+...+\frac{1}{7.8}+\frac{1}{8.9}\right)\)
= \(\frac{1}{90}-\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{7}-\frac{1}{8}+\frac{1}{8}-\frac{1}{9}\right)\)
= \(\frac{1}{90}-\left(1-\frac{1}{9}\right)\)
= \(\frac{1}{90}-\frac{8}{9}\)
= \(-\frac{79}{90}\)
\(A=\frac{1}{90}-\frac{1}{72}-\frac{1}{56}-\frac{1}{42}-\frac{1}{30}-\frac{1}{20}-\frac{1}{12}-\frac{1}{6}-\frac{1}{2}\)
\(A=\frac{1}{90}-\left(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+\frac{1}{42}+\frac{1}{56}+\frac{1}{72}\right)\)
\(A=\frac{1}{90}-\left(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}+\frac{1}{7.8}+\frac{1}{8.9}\right)\)
\(A=\frac{1}{90}-\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-........-\frac{1}{8}+\frac{1}{8}-\frac{1}{9}\right)\)
\(A=\frac{1}{90}-\left(1-\frac{1}{9}\right)\)
\(A=\frac{1}{90}-\frac{8}{9}\)
\(A=\frac{1}{90}-\frac{80}{90}\)
\(A=-\frac{79}{90}\)
Nguồn :Câu hỏi của Nguyễn Thị Bích Vân - Toán lớp 7 - Học toán với OnlineMath
_Minh ngụy_
Tính bằng cách hợp lý
A, 5,4 + 6,5 + 7,6 + 8,7 - 4,4 - 5,5 - 6,6 - 7,7
B, 1/2+ 1/6 + 1/12 + 1/20+1/30+1/42+1/56+1/72+1/90
a) = ( 5,4 - 4,4 ) + ( 6,5 - 5,5 ) + ( 7,6 - 6,6 ) + ( 8,7 - 7,7 )
= 1 + 1 + 1 + 1
= 4
b) = 9/10
Tinh cách hợp lý
A= 1/90 —1/72—1/56 —1/42 —1/30—1/20—1/12—1/6—1/2
A = 1/90 - 1/72 - 1/56 - ... - 1/6 - 1/2
A = 1/90 - (1/2 + 1/6 + ... + 1/56 + 1/72)
A = 1/90 - (1/1.2 + 1/2.3 + ... + 1/7.8 + 1/8.9)
A = 1/90 - (1 - 1/2 + 1/2 - 1/3 + ... + 1/7 - 1/8 + 1/8 - 1/9)
A = 1/90 - (1 - 1/9)
A = 1/90 - 8/9
A = 1/90 - 80/90
A = -79/90
A = 1/90 - 1/72 - 1/56 - ... - 1/6 - 1/2
A = 1/90 - (1/2 + 1/6 + ... + 1/56 + 1/72)
A = 1/90 - (1/1.2 + 1/2.3 + ... + 1/7.8 + 1/8.9)
A = 1/90 - (1 - 1/2 + 1/2 - 1/3 + ... + 1/7 - 1/8 + 1/8 - 1/9)
A = 1/90 - (1 - 1/9)
A = 1/90 - 8/9
A = 1/90 - 80/90
A = -79/90