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Số số hạng là :
Có số cặp là :
50 : 2 = 25 ( cặp )
Mỗi cặp có giá trị là :
99 - 97 = 2
Tổng dãy trên là :
25 x 2 = 50
Đáp số : 50
a) 213 - 2 x X = 47
2 x X = 213 - 47
2 x X = 166
X = 166 : 2
X = 83
b) 3 x ( X + 1 ) - 300 = 906
3 x ( X + 1 ) = 906 + 300
3 x ( X + 1 ) = 1206
X + 1 = 1206 : 3
X + 1 = 402
X = 402 - 1
X = 401
c) \(\frac{7}{3}-\frac{2}{3}\times x=\frac{1}{4}\)
\(\frac{2}{3}\times x=\frac{7}{3}-\frac{1}{4}\)
\(\frac{2}{3}\times x=\frac{25}{12}\)
\(x=\frac{25}{12}:\frac{2}{3}\)
\(x=\frac{25}{8}\)
d) \(\frac{2}{5}\times x+\frac{7}{8}=2\)
\(\frac{2}{5}\times x=2-\frac{7}{8}\)
\(\frac{2}{5}\times x=\frac{9}{8}\)
\(x=\frac{9}{8}:\frac{2}{5}\)
\(x=\frac{45}{16}\)
Học tốt #
a) \(213-2\cdot x=47\)\(\Leftrightarrow2\cdot x=166\Leftrightarrow x=83\)
b)\(3x\left(x+1\right)-300=906\Leftrightarrow3x\left(x+1\right)=606\)
\(\Leftrightarrow x\left(x+1\right)=202\Leftrightarrow x^2+x-202=0\)
\(\Leftrightarrow\left(x+\frac{1}{2}\right)^2-202,25=0\)\(\Leftrightarrow\orbr{\begin{cases}x+\frac{1}{2}=\sqrt{202,25}\\x+\frac{1}{2}=-\sqrt{202,25}\end{cases}}\)
\(\Leftrightarrow\orbr{\begin{cases}x=\sqrt{202,25}-0,5\\x=-\sqrt{202,25}-0,5\end{cases}}\)
\(a,x-5⋮x+2\)
\(\Rightarrow x+2-7⋮x+2\)
\(\Rightarrow x+2\inƯ\left(7\right)=\left\{\pm1;\pm7\right\}\)
x + 2 = 1=> x = -1
x + 2 = -1 => x = -3
.... tương tự nhé ~
\(2x+3⋮x-5\)
\(\Rightarrow2x-10+7⋮x-5\)
\(\Rightarrow2\left(x-5\right)+7⋮x-5\)
\(\Rightarrow x-5\inƯ\left(7\right)=\left\{\pm1;\pm7\right\}\)
x - 5 = 1 => x = 6
....
\(460+85\times4=\left(x+200\right)\times4\)
\(\left(x+200\right)\times4=460+340\)
\(\left(x+200\right)\times4=800\)
\(x+200=800:4\)
\(x+200=200\)
\(x=200-200\)
\(x=0\)
~~~
\(\left(x-7\right)\left(2x-8\right)=0\)
\(+, TH1: x - 7 = 0\)
\(x=0+7\)
\(x=7\)
\(+, TH2 : 2x - 8 = 0 \)
\(2x=0+8\)
\(2x=8\)
\(x=8:2\)
\(x=4\)
~~~
\(x-280:35=5\times54\)
\(x-8=270\)
\(x=270+8\)
\(x=278\)
~~~
\(324+16\times\left(2x+3\right)=404\)
\(16\times\left(2x+3\right)=404-324\)
\(16\times\left(2x+3\right)=80\)
\(2x+3=80:16\)
\(2x+3=5\)
\(2x=5-3\)
\(2x=2\)
\(x=2:2\)
\(x=1\)
#\(Toru\)
`460 + 85 xx 4 = ( x + 200) xx 4`
`460 + 340 = (x+200)xx4`
` 800= (x+200)xx4`
`x+200=800:4`
`x+200=200`
`x=200-200`
`x=0`
__
`(x-7)(2x-8)=0`
`@ TH1`
`x-7=0`
`x=0+7`
`x=7`
`@ TH2`
`2x-8=0`
`2x=0+8`
`2x=8`
`x=8:2`
`x=4`
__
`x -280 : 35=5xx54`
`x -280 : 35=270`
`x-8=270`
`x=270+8`
`x=278`
__
`324 + 16xx(2x+3)=404`
`16xx(2x+3)=404 -324`
`16xx(2x+3)=80`
`2x+3=80:16`
`2x+3=5`
`2x=5-3`
`2x=2`
`x=2:2`
`x=1`
\(\left(\frac{7}{2}+2x\right).\frac{8}{3}=\frac{16}{3}\)
\(\frac{7}{2}+2x=\frac{16}{3}:\frac{8}{3}\)
\(\frac{7}{2}+2x=2\)
\(2x=2-\frac{7}{2}\)
\(2x=\frac{-3}{2}\)
\(x=\frac{-3}{2}:2\)
\(x=\frac{-3}{4}\)
\(\frac{1}{3}.x+0,5x=0,75\)
\(\frac{1}{3}x+\frac{1}{2}x=\frac{3}{4}\)
\(x.\left(\frac{1}{3}+\frac{1}{2}\right)=\frac{3}{4}\)
\(x.\frac{5}{6}=\frac{3}{4}\)
\(x=\frac{3}{4}:\frac{5}{6}\)
\(x=\frac{9}{10}\)
a) 1/1.2 + 1/2.3 + 1/3.4 + .... + 1/x.(x+1) = 499/500
1 - 1/2 + 1/2 - 1/3 + 1/3 - 1/4 + .... + 1/x - 1/x+1 = 499/500
1 - 1/x+1 = 499/500
1/x+1 = 1 - 499/500
1/x+1 = 1/500
x + 1 = 500
x = 500 - 1
x = 499
b) 1/1.3 + 1/3.5 + 1/5.7 + .... + 1/x.(x+2) = 20/41
1/2 . [ 2/1.3 + 2/3.5 + 2/5.7 + ... + 2/x.(x+2) ] = 20/41
1/2 . [ 1 - 1/3 + 1/3 - 1/5 + 1/5 - 1/7 + ... + 1/x - 1/x+2 ] = 20/41
1/2 . [ 1 - 1/x+2 ) = 20/41
1 - 1/x+2 = 20/41 : 1/2
1 - 1/x+2 = 40/41
1/x+2 = 1 - 40/41
1/x+2 = 1/41
x + 2 = 41
x = 41 - 2
x = 39
\(2x+7=x+5\)
\(\Rightarrow2x+7-x=5\)
\(\Rightarrow x=5-7=-2\)
2x - 7 = 1
2x = 1 + 7
2x = 8
x = 8 : 2
x = 4
Đ/s: ...
2x - 7 = 1
2x = 1 +7
2x = 8
x = 8 : 2
x = 4