tinh nhanh
a) A=(-1).(-1)^2.(-1)^3.(-1)^4....(-1)^2010.(-1)^2011
b) B=70.(131313/565656+131313/727272+131313/909090)
d)D= -1/20+ -1/30+ -1/42+ -1/56+ -1/72+ -1/90
e) E= 5/2.1+4/1.11+3/11.2+1/2.15+13/15.4
Thực hiện phép tính để tính giá trị các biểu thức sau:
\(a,A=\left(\frac{136}{15}-\frac{28}{5}+\frac{62}{10}\right).\frac{21}{24}\)
\(b,B=70.\left(\frac{131313}{565656}+\frac{131313}{727272}+\frac{131313}{909090}\right)\)
\(c,C=\frac{5}{2.1}+\frac{4}{1.11}+\frac{3}{11.2}+\frac{1}{2.15}+\frac{13}{15.4}\)
a) A= ( 136/15 - 28/5 + 62/10) .21/24
A= (136/15 - 84/15 + 93/15) . 7/8
A= 145/15. 7/8
A= 203/24
b) B= 70 .( 131313.565656 + 131313/727272 + 131313/ 909090)
= 70. ( 13/56+ 13/72 + 13/90)
= 70 . 39/70
= 39
không quy đồng hãy tính hợp lý:
A= -1:20+ -1:30+ -1:42+ -1:56+ -1:72+ -1:90
B = 5:2.1+4:1.11+2:11.2+3:2.15+1:2.15+13:15.4
\(A=-\left(\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}+\frac{1}{7.8}+\frac{1}{8.9}+\frac{1}{9.10}\right)\)
\(A=-\left(\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+...+\frac{1}{9}-\frac{1}{10}\right)\)
\(A=-\left(\frac{1}{4}-\frac{1}{10}\right)=\frac{-3}{20}\)
a,A= (-1)*(-2)*(-3)*(-4)*...*(-2019)
b,B=1/1*2+1/2*3+1/3*4+...+1/98*99+1/99*100
c,C=2^10*13+2^10*65/2^8*104
d,D=70*(131313/565656+131313/727272+131313/909090)
Không dùng máy tinh bỏ túi.Tính hợp lí:
a,4/2.4+4/4.6+4/6.8+......+4/2012.2014
b,5/2.1+4/1.11+3/11.2+1/2.15+13/15.4
c,(2/3+2/7-1/14):(-1-3/7+3/28)
d,1/10+-1/20+-1/30+-1/42+-1/56+-1/72+-1/90
a,A=4/2.4+4/4.6+4/6.8+......+4/2012.2014
\(\Rightarrow\frac{1}{2}A=\frac{2}{2\cdot4}+\frac{2}{4\cdot6}+...+\frac{2}{2012\cdot2014}\)
\(\Rightarrow\frac{1}{2}A=\frac{1}{2}-\frac{1}{4}+\frac{1}{4}-\frac{1}{6}+...+\frac{1}{2012}-\frac{1}{2014}\)
\(\Rightarrow\frac{1}{2}A=\frac{1}{2}-\frac{1}{2014}\)
\(\Rightarrow A=1-\frac{1}{1007}\)
\(\Rightarrow A=\frac{1006}{1007}\)
\(\dfrac{-1}{20}\)+\(\dfrac{-1}{30}\)+\(\dfrac{-1}{42}\)+\(\dfrac{-1}{56}\)+\(\dfrac{-1}{72}\)+\(\dfrac{-1}{90}\)=
\(\dfrac{5}{2.1}\)+\(\dfrac{4}{1.11}\)+\(\dfrac{3}{11.2}\)+\(\dfrac{1}{2.15}\)+\(\dfrac{13}{15.4}\)=
cíu mình 2 bài này với mình ko biết làm
Bài 1 : Không quy đồng hãy tính hợp lý các tổng sau :
a, A = -1/20+-1/30 + -1/42 + -1/56 + -1/72 + -1/90
b, B = 5/2.1 +4/1.11 + 3/11.2 + 1/ 2.15 + 13/15.4
A = - (1/4.5 + 1/5.6 + 1/6.7 + 1/7.8 + 1/8.9 +1/9.10)
A = -( 1/4 - 1/5 + 1/5 - 1/6 + 1/6 - 1/7 + 1/7 - 1/8 + 1/8 - 1/9 + 1/9 - 1/10)
A = -( 1/4 - 1/10)
A = -3/20
B = 7(5/2.7 + 4/7.11 + 3/11.14 + 1/14.15 + 13/15.28)
B = 7(1/2 - 1/7 + 1/7 - 1/11 +......+ 1/15 - 1/28)
B = 7(1/2 - 1/28)
B = 7 . 13/28
B = 13/4
nguyễn mai phương đúng rồi đó các bạn
Câu 1.Tính giá trị các biểu thức sau :
a) A = (-1).(-1)2.(-1)3.(-1)4...(-1)2010.(-1)2011
b) B = 70.(131313 : 565656 + 131313 : 727272 + 131313 : 909090)
c) C = 2a : 3b + 3b : 4c + 4c : 5d + 5d : 2a biết 2a : 3b = 3b : 4c = 4c : 5d = 5d :2a
trả lời khẩn cấp nha!!!
tính các giá trị biểu thức sau
a)A= (-1).(-1)2.(-1)3.(-1)4.(-1)5.(-1)6.(-1)7....(-1)2010.(-1)2011
b) B= 70 . (131313/565656+ 131313/727272+131313/909090)
c) C= 2a/3b+3b/4c+4c/5d+5d/2a biết 2a/3b= 3b/4c=4c/5d=5d/2a
Bài 1:Tính nhanh
a)\(\dfrac{-1}{20}+\dfrac{-1}{30}+\dfrac{-1}{42}+\dfrac{-1}{56}+\dfrac{-1}{72}+\dfrac{1}{9.10}\)
b)\(\dfrac{5}{2.1}+\dfrac{4}{1.11}+\dfrac{3}{11.2}+\dfrac{1}{2.15}_{_{_{_{_{_{_{_{_{_{_{_{_{_{_{_{_{_{_{_{_{_{_{_{_{++++=}}}}}}}}}}}}}}}}}}}}}}}}}+\dfrac{13}{15.4}\)
Lời giải:
a, Đặt \(A=\dfrac{-1}{20}+\dfrac{-1}{30}+\dfrac{-1}{42}+\dfrac{-1}{56}+\dfrac{-1}{72}+\dfrac{-1}{90}\)
\(\Rightarrow A=\dfrac{-1}{4.5}+\dfrac{-1}{5.6}+\dfrac{-1}{6.7}+...+\dfrac{-1}{9.10}\)
\(\Rightarrow A=\dfrac{-1}{4}+\dfrac{1}{5}-\dfrac{1}{5}+...-\dfrac{1}{9}+\dfrac{1}{10}\)
\(\Rightarrow A=\dfrac{-1}{4}+\dfrac{1}{10}\)
\(\Rightarrow A=\dfrac{-3}{20}\)
\(\dfrac{-1}{20}+\dfrac{-1}{30}+\dfrac{-1}{42}+\dfrac{-1}{56}+\dfrac{-1}{72}+\dfrac{-1}{9.10}\\ =\dfrac{-1}{4.5}+\dfrac{-1}{5.6}+\dfrac{-1}{6.7}+\dfrac{-1}{7.8}+\dfrac{-1}{8.9}+\dfrac{-1}{9.10}\)
\(=\dfrac{-1}{4}-\dfrac{-1}{5}+\dfrac{-1}{5}-\dfrac{-1}{6}+\dfrac{-1}{6}-\dfrac{-1}{7}+\dfrac{-1}{7}-\dfrac{-1}{8}+\dfrac{-1}{8}-\dfrac{-1}{9}+\dfrac{-1}{9}-\dfrac{-1}{10}\)
\(=\dfrac{-1}{4}-\dfrac{-1}{10}\\=\dfrac{-1}{4}+\dfrac{1}{10}\\=\dfrac{-5}{20}+\dfrac{2}{20}\\=\dfrac{-3}{20}\)