a) 12 2/5 < y < 13 1/7
22/5 x 2 > y > 6 1/2
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a, \(\frac{5}{11.16}+\frac{5}{11.21}+\frac{5}{21.26}+...+\frac{5}{61.66}\)
=\(\frac{1}{11}-\frac{1}{16}+\frac{1}{16}-\frac{1}{21}+\frac{1}{21}-\frac{1}{26}+...+\frac{1}{61}-\frac{1}{66}\)
=\(\frac{1}{11}-\frac{1}{66}=\frac{5}{66}\)
a, A=1/11-1/16+1/16-1/21+1/21-1/26+...+1/61-1/66
= 1/11-1/66=5/66 ( A chính là biểu thức ở phần a)
b, 1/12+1/20+1/30+...+1/110
=1/3.4+1/4.5+1/5.6+..+1/10.11
=1/3-1/4+1/4-1/5+1/5-1/6+...+1/10-1/11
=1/3-1/11=8/33
a) \(x^2+y^2=\left(x+y\right)^2-2xy=1^2-2.\left(-6\right)=13\)
\(x^3+y^3=\left(x+y\right)^3-3xy\left(x+y\right)=1^3-3.\left(-6\right).1=19\)
\(x^5+y^5=\left(x^2+y^2\right)\left(x^3+y^3\right)-x^2y^2\left(x+y\right)=13.19-\left(-6\right)^2.1=211\)
b) \(x^2+y^2=\left(x-y\right)^2+2xy=1^1+2.6=13\)
\(x^3-y^3=\left(x-y\right)^3+3xy\left(x-y\right)=1^3+3.6.1=19\)
\(x^5-y^5=\left(x^2+y^2\right)\left(x^3-y^3\right)+x^2y^2\left(x-y\right)=13.19+6^2.1=283\)
Đặt \(\frac{x}{2}=\frac{y}{3}=\frac{z}{5}=k\Rightarrow x=2k,y=3k,z=5k\)
Ta có: xyz = 810 => 2k.3k.5k = 810 => 30k3 = 810 => k3 = 27 => k = 3
=> x = 6, y = 9, z = 15
1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+20=210
1+2+3+4+5+6+7=28
a)dãy trên có 20 số hạng , vậy tổng là:
(20 + 1) x 20 : 2 = 210
b) làm tương tự bài a
Tìm x . biết :
\(a,\frac{2}{5}:\left(-x-\frac{1}{2}\right)=\frac{4}{5}\)
\(\Rightarrow-x-\frac{1}{2}=\frac{2}{5}:\frac{4}{5}\)
\(\Rightarrow-x-\frac{1}{2}=\frac{2}{5}.\frac{5}{4}\)
\(\Rightarrow-x-\frac{1}{2}=\frac{1}{2}\)
\(\Rightarrow-x=\frac{1}{2}+\frac{1}{2}\)
\(\Rightarrow-x=1\)
\(\Rightarrow x=-1\)
Vậy \(x=-1\)
a. \(\frac{2}{5}.\left(-x-\frac{1}{2}\right)=\frac{4}{5}\)
\(\Rightarrow-x-\frac{1}{2}=\frac{2}{5}:\frac{4}{5}\)
\(\Rightarrow-x-\frac{1}{2}=\frac{2}{5}.\frac{5}{4}\)
\(\Rightarrow-x-\frac{1}{2}=\frac{1}{2}\)
\(\Rightarrow-x=\frac{1}{2}+\frac{1}{2}\)
\(\Rightarrow-x=1\)
\(\Rightarrow x=-1\)
A , 34 - \(\dfrac{x}{30}\) = \(\dfrac{5}{6}\)
\(\dfrac{x}{30}\) = 34 - \(\dfrac{5}{6}\)
\(\dfrac{x}{30}=\) \(\dfrac{199}{6}\)
\(\dfrac{x}{30}=\) \(\dfrac{995}{30}\)
x = 995
B x +\(\dfrac{13}{34}\) = \(\dfrac{12}{17}\)
x = \(\dfrac{12}{17}-\dfrac{13}{34}\)
x = \(\dfrac{11}{34}\)
\(\dfrac{7}{9}=\dfrac{21}{27};\dfrac{7}{10}=\dfrac{21}{30}\)
hai số nằm giữa \(\dfrac{7}{9}\) và \(\dfrac{7}{10}\)
\(\dfrac{21}{27}>\dfrac{21}{28}>\dfrac{21}{29}>\dfrac{21}{30}\)
a) 3/4 + -1/8 = 5/8
b)-5/12 + -7/24 = -9/8
c) 4/21 - -5/28 = 31/84
d) 1 + -7/28 = 3/4
e) -4/3 - 17/6= -25/6
f) 1/3 - ( 1/2 +1/8 )= -7/24
g)1/21 - ( 1/7 - 1/3 ) = 5/21
h)1/2 - 1/4 + 1/13 + 1/8= 47/104
a) x - 1/10 = 1/15
x=1/15+1/10
x=1/6 Vay x=1/6b) -4/21 - x = -3/7
x=-4/21+3/7 x=5/21 Vay x=5/21c) x + 1/2 = 3/4 - (-1/2)
x+1/2= 5/4
x= 5/4-1/2
x=3/4
Vay x=3/4
d) 4/7 - x = 1/3 - (-2/3)
x= 4/7-1/3-2/3 x= -3/7 Vay x=-3/7
a, 12 2/5 < y < 13 1/7
(=) 12,4 < y < 13,1428...
vì y là 1 số tự nhiên
=) y = 13
b, 22/5 x 2 > y > 6 1/2
8,8 > y > 6,5
vì y là 1 số tự nhiên
=) y = 7 hoặc 8
chúc bn học tốt
a)=>y=435/35;436/35437/35;438/35439/35;440/35;441/35;442/35;443/35;444/35;445/35;446/35;447/35;448/35;449/35;450/35;451/35;
452/35;453/35;454/35.
22/5x2>y>6 1/2
87/10;86/10;85/10;84/10;83/10;82/10;81/10;80/10;79/10;78/10;77/10;76/10;75/10;74/10;73/10;72/10;71/10;70/10;69/10;68/10;67/10;
66/10.