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B2"
`a)3/4+1/2-1/4`
`=3/4-1/4+1/2`
`=1/2+1/2=1`
`b)(-2)/3*5/7+(-2)/3*2/7+5/3`
`=(-2)/3*(5/7+2/7)+5/3`
`=-2/3+5/3=1`
`c)(-5)/9+5/9:(1 2/3-2 1/6)`
`=(-5)/9+5/9:(5/3-13/6)`
`=(-5)/9+5/9:(-3)/6`
`=(-5)/9+5/9*(-2)`
`=5/9*(-1-2)`
`=5/9*(-3)=-5/3`
b3:
`a)x*3/6=2/3`
`=>x*1/2=2/3`
`=>x=4/3`
`b)x/150=5/6*(-7)/25`
`=>x/150=(-7)/(6*5)=-7/30`
`=>x/150=(-35)/150`
`=>x=-35`
`c)1/2x+3/5x=3`
`=>11/10x=3`
`=>x=3*10/11=30/11`
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Dạng 3:
Bài 1:
a) Số lượng số hạng là:
\(\left(999-1\right):1+1=999\) (số hạng)
Tổng dãy là:
\(A=\left(999+1\right)\cdot999:2=499500\)
b) Số lượng số hạng là:
\(\left(100-7\right):3+1=32\) (số hạng)
Tổng dãy là:
\(S=\left(100+7\right)\cdot32:2=1712\)
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b: \(\sqrt{8^2+6^2}-\sqrt{16}+\dfrac{1}{2}\sqrt{\dfrac{4}{25}}\)
\(=10-4+\dfrac{1}{2}\cdot\dfrac{2}{5}=6+\dfrac{1}{5}=\dfrac{31}{5}\)
F,\(\frac{3}{4}x-\frac{1}{4}=2\left(x-\frac{7}{4}\right)+\frac{1}{4}x\)
\(\frac{3}{4}x-\frac{1}{4}=2x-\frac{14}{4}+\frac{1}{4}\)
\(\frac{3}{4}x-\frac{1}{4}-2x+\frac{14}{4}-\frac{1}{4}=0\)
\(\frac{3}{4}x-2x-\frac{1}{4}+\frac{14}{4}-\frac{1}{4}=0\)
\(\frac{-5}{4}x-3=0\)
\(-\frac{5}{4}x=3\)
\(x=-\frac{12}{5}\)
G,
\(\text{|3x - 2 | - | 7x + 8 | = 0}\)
\(\Rightarrow\text{|3x - 2 | =0 hoặc | 7x + 8 | = 0}\)
\(\text{3x - 2 = 0}\) \(7x+8=0\)
\(x=\frac{2}{3}\) \(x=\frac{-8}{7}\)
H, \(x-\frac{20}{11.13}-\frac{20}{13.15}-...-\frac{20}{53.55}=\frac{3}{11}\)
\(x-10.\left(\frac{2}{11.13}+\frac{2}{13.15}+...+\frac{2}{53.55}\right)=\frac{3}{11}\)
\(x-10.\left(\frac{2}{11}-\frac{2}{13}+\frac{2}{13}-\frac{2}{15}+...+\frac{2}{53}-\frac{2}{55}\right)=\frac{3}{11}\)
\(x-10.\left(\frac{2}{11}-\frac{2}{55}\right)=\frac{3}{11}\)
\(x-10.\frac{8}{55}=\frac{3}{11}\)
\(x-\frac{16}{11}=\frac{3}{11}\)
\(x=\frac{19}{11}\)