Đáp án:
Bài 1:
`a)` `132/175` `b) -18 c) -14 d) 9 e) ??`
Bài 2:
`a) x=-2` `b)` `x=-19/6` `c) x=4` hoặc `x=0`
`d)` `x=19/25` hoặc `x=26/25` `e)` `x=-47/30` `f) x=1` hoặc `x=-2/3`
Giải thích các bước giải:
Bài 1:
`a)` `12/25*23/7-12/25*12/7`
`=12/25*(23/7-12/7)`
`=12/25*11/7`
`=132/175`
`b)` `13 2/7:(-8)/9+2 5/7:(-8)/9`
`=(13 2/7+2 5/7):(-8)/9`
`=(13+2+(2+5)/7)*(-9)/8`
`=(15+1)*(-9)/8`
`=-(16*9)/8`
`=-2*9`
`=-18`
`c)` `(-6)/11*7/10*11/(-6)*(-20)`
`=((-6)/11*11/(-6))*(-20*7/10)`
`=-2*7`
`=-14`
`d)` `(-1 1/2):3/4*(-4 1/2)`
`=-3/2*4/3*(-9)/2`
`=9`
`e)` `2+(1)/(2+(1)/(2+1/(2+1/2)`
Câu này mình chưa gặp bao giờ nên bỏ qua nhé (bất đắc dĩ), sorry bạn Tus nhiều ;<
Sau mà biết làm thì mình sẽ bổ sung sau nha, cảm ơn.
Bài 2:
`a)` `3/7x-2/3x=10/21`
`⇒(3/7-2/3)x=10/21`
`⇒ x=10/21:(9-14)/(3*7)`
`⇒ x=10/21*21/(-5)`
`⇒ x=-2`
Vậy `x=-2`
`b)` `7/35:(x-1/3)=-2/35`
`⇒ x-1/3 =7/35:(-2)/35`
`⇒ x =1/3-7/35*35/2`
`⇒ x =1/3-7/2`
`⇒ x =(2-21)/(3*2)`
`⇒ x =(-19)/6`
Vậy `x=-19/6`
`c)` `|2x-4|+1=5`
`⇒|2x-4| =4`
`⇒`\(\left[ \begin{array}{l}2x-4=4\\2x-4=-4\end{array} \right.\) `⇒`\(\left[ \begin{array}{l}2x=4+4\\2x=4-4\end{array} \right.\) `⇒`\(\left[ \begin{array}{l}x=\dfrac{8}{2}\\x=\dfrac{0}{2}\end{array} \right.\) `⇒`\(\left[ \begin{array}{l}x=4\\x=0\end{array} \right.\)
Vậy `x=4` hoặc `x=0`
`d)` `3|3-2x|-1=2/5`
`⇒ 3|3-2x| =2/5+1`
`⇒ |3-2x| =(2+5)/5:3`
`⇒ |3-2x| =7/5*1/3`
`⇒ |3-2x| =7/15`
`⇒`\(\left[ \begin{array}{l}3-2x=\dfrac{7}{15}\\3-2x=-\dfrac{7}{15}\end{array} \right.\)
`⇒`\(\left[ \begin{array}{l}2x=3-\dfrac{7}{15}\\2x=3+\dfrac{7}{15}\end{array} \right.\)
`⇒`\(\left[ \begin{array}{l}x=\dfrac{45-7}{15}:2\\x=\dfrac{45+7}{15}:2\end{array} \right.\)
`⇒`\(\left[ \begin{array}{l}x=\dfrac{38}{15}.\dfrac{1}{2}\\x=\dfrac{52}{15}.\dfrac{1}{2}\end{array} \right.\)
`⇒`\(\left[ \begin{array}{l}x=\dfrac{19}{15}\\x=\dfrac{26}{15}\end{array} \right.\)
Vậy `x=19/25` hoặc `x=26/15`
`e)` `3(x-1/2)-5(x+3/5)=-x+1/5`
`⇒3x-3*1/2-5x-5*3/5-x=1/5`
`⇒(3x-5x-x)-3/2-3 =1/5`
`⇒-3x =1/5+3/2+3`
`⇒ x =(2+15+30)/(2*5):(-3)`
`⇒ x =47/10*(-1)/3`
`⇒ x =-47/30`
Vậy `x=-47/30`
`f)` `(2x-2)(x+2/3)=0`
`⇒`\(\left[ \begin{array}{l}2x-2=0\\x+\dfrac{2}{3}=0\end{array} \right.\) `⇒`\(\left[ \begin{array}{l}2x=2\\x=-\dfrac{2}{3}\end{array} \right.\) `⇒`\(\left[ \begin{array}{l}x=\dfrac{2}{2}=1\\x=-\dfrac{2}{3}\end{array} \right.\)
Vậy `x=1` hoặc `x=-2/3`
_______________________
#phamuyen15032008
