Tính nhanh :
3/9 x 77/79 + 3/9 x 2/79
(1/2 +1/3 + 1/4 +....+1/80) x> 1/79 + 2/78 + 3/77 +...+ 78/2 + 79/1)
=>(1/2+1/3+...+1/80)*x>(1+1/79+1+2/78+...+1+78/2+1)
=>\(x\left(\dfrac{1}{2}+\dfrac{1}{3}+...+\dfrac{1}{80}\right)>\dfrac{80}{80}+\dfrac{80}{79}+...+\dfrac{80}{3}+\dfrac{80}{2}\)
=>x>80
tính nhanh:
1 + ( -2 ) + 3 + ( -4 ) + 5 +......77 + ( -78 ) + 79 + (-80 )
nhanh nha mình cần gấp
\(1+\left(-2\right)+3+\left(-4\right)+5+...+77+\left(-78\right)+79+\left(-80\right)\)
\(=\left[1+\left(-2\right)\right]+\left[3+\left(-4\right)\right]+\left[5+\left(-6\right)\right]+...+\left[77+\left(-78\right)\right]+\left[79+\left(-80\right)\right]\)
\(=-1+\left(-1\right)+\left(-1\right)+...+\left(-1\right)\)
Từ 1 -> 80 có số số hạng là: (80-1):1+1=80 số hạng
=> Có 80:2=40 số -1
\(=-1\cdot40=-40\)
Đặt: \(A=1+\left(-2\right)+3+\left(-4\right)+...+77+\left(-78\right)+79+\left(-80\right)\)
\(\Rightarrow A=1-2+3-4+...+77-78+79-80\)
\(\Rightarrow A=-1-1-...-1-1\) ( \(40\)cặp)
\(\Rightarrow A=-1\times40=-41\)
1+(-2)+3+(-4)+5+...+77+(-78)+79+(-80)
=(2-1)+(4-3)+(6-5)+...+(78-77)+(80-79)
=1+1+1+...+1+1
=40.1
=40
Tính nhanh
71+72+73+74+75+76+77+78+79
tìm x
X x 7 +X x 2 = 108
71 + 72 + 73 + 74 + 75 + 76 + 77 + 78 + 79
= ( 71 + 79 ) + ( 72 + 78 ) + ( 73 + 77 ) + ( 74 + 76 ) + 75
= 150 + 150 + 150 + 150 + 75
= 150 x 4 + 75
= 600 + 75
= 675
Tìm x :
X x 7 + X x 2 = 108
X x ( 7 + 2 ) = 108
X x 9 = 108
X = 108 : 9
X = 12
\(71+72+73+74+75+76+77+78+79\)
\(=\left(71+79\right)+\left(72+78\right)+\left(73+77\right)+\left(74+76\right)+75\)
\(=150+150+150+150+75\)
\(=600+75\)
\(=675\)
\(X\)x\(7+X\)x\(2=108\)
\(X\)x\(\left(7+2\right)=108\)
\(X\)x\(9=108\)
\(X=108:9\)
\(X=12\)
Vậy \(X=12\)
\(71+72+73+74+75+76+77+78+79\)
\(=\left(71+79\right)+\left(72+78\right)+\left(73+77\right)+\left(74+76\right)+75\)
\(=150+150+150+150+75\)
\(=150.4+75=600+75=675\)
\(7x+2x=108\Leftrightarrow x\left(7+2\right)=108\Leftrightarrow9x=108\)
\(\Leftrightarrow x=108:9\Leftrightarrow x=12\)
Tính nhanh;
a , 4*(2*29*39+2*59*79)/ 9*29*39+9*59+79-29*39-59*79
Dấu * là nhân còn /là dấu gạch giữa tử số và mẫu số
\(\frac{4x\left(2x29x39+2x59x79\right)}{9x29x39+9x59x79-29x39-59x79}\) =
\(\frac{8x29x39+8x59x79}{29x39x\left(9-1\right)+59x79x\left(9-1\right)}\) =
\(\frac{8x29x39+8x59x79}{29x39x8+59x79x8}\)= \(1\)
6) x-1/2=9/2
7) x+5/4=-3/4
8) x+2/7=5/7
9) x-4/3=1/3
10) x+5/2=-7/2
6, \(x=\dfrac{9}{2}+\dfrac{1}{2}=\dfrac{10}{2}=5\)
7, \(x=-\dfrac{3}{4}-\dfrac{5}{4}=-\dfrac{8}{4}=-2\)
8, \(x=\dfrac{5}{7}-\dfrac{2}{7}=\dfrac{3}{7}\)
9, \(x=\dfrac{1}{3}+\dfrac{4}{3}=\dfrac{5}{3}\)
10, \(x=-\dfrac{7}{2}-\dfrac{5}{2}=-\dfrac{12}{2}=-6\)
\(6,x-\dfrac{1}{2}=\dfrac{9}{2}\Leftrightarrow x=5\)
\(7,x+\dfrac{5}{4}=\dfrac{-3}{4}\Leftrightarrow x=-2\)
\(8,x+\dfrac{2}{7}=\dfrac{5}{7}\Leftrightarrow x=\dfrac{3}{7}\)
\(9,x-\dfrac{4}{3}=\dfrac{1}{3}\Leftrightarrow x=\dfrac{5}{3}\)
\(10,x+\dfrac{5}{2}=\dfrac{-7}{2}\Leftrightarrow x=-6\)
\(x-\dfrac{1}{2}=\dfrac{9}{2}\)
\(x\) \(=\dfrac{9}{2}+\dfrac{1}{2}=\dfrac{10}{2}=5\)
\(x+\dfrac{5}{4}=\dfrac{-3}{4}\)
\(x\) \(=\dfrac{-3}{4}+\dfrac{-5}{4}=\dfrac{-8}{4}=-2\)
\(x+\dfrac{2}{7}=\dfrac{5}{7}\)
\(x\) \(=\dfrac{5}{7}+\dfrac{-2}{7}=\dfrac{3}{7}\)
\(x-\dfrac{4}{3}=\dfrac{1}{3}\)
\(x\) \(=\dfrac{1}{3}+\dfrac{4}{3}=\dfrac{5}{3}\)
\(x+\dfrac{5}{2}=\dfrac{-7}{2}\)
\(x\) \(=\dfrac{-7}{2}+\dfrac{-5}{2}=\dfrac{-12}{2}=-6\)
tim x de: (x+1)+(x+3)+(x+5)+...+(x+77)+(x+79)=120
(ghi lại đề)=(x+x+x+....+x)+(1+3+5+...+79)=x+x+x+.......x+1600=120
-->x+x+x+...+x=-1480
x=-1480/37(vì có 37 số hạng)
-->x=-40
Tính hợp lí
a, -2/5×4/7+-3/5×2/7+-3/5
b,5/9×14/17+1/17×5/9+2/9+5/12
c,-4/25÷11/79+15/11÷25/79
d, (2/101÷5/9+-3/7)×(6/5÷1/3)
(1+2+3+4+5+6+79+8+9) * 0 + ? 9 nho phai tra loi nhanh nhat do nha)
*Tính Nhanh :
1 . 12 . 53 + 53 . 172 - 53 . 84 .
2 .33 . 77 + 66 . 77+ 77 .
3 . 79 . 35 + 79 . 77 + 21 . 83 + 21 . 29 .
Bạn nào làm đúng và nhanh mình tick cho nha
Mình cần gấp !!!
Thanks
a) \(12.53+53.172-53.84=53.\left(12+172-84\right)=53.100=5300\)
b) \(33.77+66.77+77=77.\left(33+66+1\right)=77.100=7700\)
c) \(79.35+79.77+21.83+21.29=79.\left(35+77\right)+21.\left(83+29\right)\)
\(=79.112+21.112=112\left(79+21\right)=112.100=11200\)
53.(12+172-84)
=53.100=5300 tương tự còn lại tự làm