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\(\frac{-1}{3}:\frac{-5}{6}=\frac{-1}{3}\times\frac{-6}{5}=\frac{2}{5}\)
@muối
#)Giải :
\(\left(\frac{1}{2}\right)^{15}\div\left(\frac{1}{4}\right)^{20}=\left(\frac{1}{2}\right)^{15}\div\left(\frac{1}{2}\right)^{40}=\left(\frac{1}{2}\right)^{-25}\)
\(1+3+5+......+x=2500\)
\(\Rightarrow\left[\left(x-1\right):2+1\right].\left(x+1\right):2=2500\)
\(\Rightarrow\left(\frac{x}{2}-\frac{1}{2}+1\right).\left(x+1\right)=2500.2\)
\(\Rightarrow\left(\frac{x}{2}+\frac{1}{2}\right).\left(x+1\right)=5000\)
\(\Rightarrow\frac{x^2}{2}+\frac{1}{2}x+\frac{x}{2}+\frac{3}{2}=5000\)
\(\Rightarrow\frac{x^2+x+x+3}{2}=5000\)
\(\Rightarrow x^2+2x+3=5000.2\)
\(\Rightarrow x^2+2x.1+1^2+3-1^2=10000\)
\(\Rightarrow\left(x+1\right)^2+2=10000\)
\(\Rightarrow\left(x+1\right)^2=10000-2\)
\(\Rightarrow\left(x+1\right)^2=9998\)
\(\Rightarrow x+1=\sqrt{9998}\)
\(\Rightarrow x=\sqrt{9998}-1\)
3⁷ . 27⁵ . 81³
= 3⁷ . (3³)⁵ . (3⁴)³
= 3⁷ . 3¹⁵ . 3¹²
= 3⁷⁺¹⁵⁺¹²
= 3³⁴
a, 33.( 17- 5) - 17.( 33-5)
= 33.17 - 33.5 - 17.33 + 17.5
= ( 33.17 - 17.33) - ( 33.5 - 17.5)
= 0 - 5.( 33- 17)
= - 5. 16
= - 80
b, 12 + 3.{ 90 : [ 39 - ( 23 - 5)2]
= 12 + 3. { 90 : [ 39 - ( 8-5)2 ]}
= 12 + 3 . { 90 : [ 39 - 32 ]}
= 12 + 3.{ 90 : (39 -9)}
= 12 + 3. { 90 : 30}
= 12 + 3 . 3
= 12 + 9
= 21
c, 307 - [ (180 .40 - 160 ) : 22 + 9] : 2
= 307 - [ ( 180 - 160) : 4 + 9]:2
= 307 - [ 20:4 +9 ] :2
= 307 - [ 5 + 9] : 2
= 307 - 14 : 2
= 307 - 7
= 300
3+5+7+...+77+79+100=
(3+5+7+...+77+79)+100=
{(3+79).[(79-3)/2+1]/2} + 100=
{82.[76/2+1]/2} + 100=
{82.[38+1]/2} + 100=
{82.39/2} + 100=
{82.19,5}+ 100=
{82.19,5}+ 100=
1599+100=
1699