Đáp án+Giải thích các bước giải:
`d)`
`(6)/(1.4)+(6)/(4.7)+(6)/(7.10)+...+(6)/(46.49)`
`=2.((3)/(1.4)+(3)/(4.7)+(3)/(7.10)+...+(3)/(46.49))`
`=2.(1-1/4+1/4-1/7+1/7-1/10+....+1/46-1/49)`
`=2.(1-1/49)`
`=2.(49/49-1/49)`
`=2. 48/49`
`=96/49`
`b)`
`2.(x+5/2)^2-5/12=1/12`
`<=>2.(x+5/2)^2=1/12+5/12`
`<=>2.(x+5/2)^2=6/12=1/2`
`<=>(x+5/2)^2=1/2 :2`
`<=>(x+5/2)^2=1/2 . 1/2`
`<=>(x+5/2)^2=1/4=(± 1/2)^2`
`<=>`\(\left[ \begin{array}{l}x+\dfrac{5}{2}=\dfrac{1}{2}\\x+\dfrac{5}{2}=-\dfrac{1}{2}\end{array} \right.\)
`<=>`\(\left[ \begin{array}{l}x=\dfrac{1}{2}-\dfrac{5}{2}\\x=-\dfrac{1}{2}-\dfrac{5}{2}\end{array} \right.\)
`<=>`\(\left[ \begin{array}{l}x=\dfrac{-4}{2}=-2\\x=\dfrac{-6}{2}=-3\end{array} \right.\)
Vậy `x=-2` hoặc `x=-3`
`c)`
`(x-2)/(4)=(11-x)/(8)`
`<=>8.(x-2)=4.(11-x)`
`<=>8x-16=44-4x`
`<=>8x+4x=44+16`
`<=>12x=60`
`<=>x=60:12`
`<=>x=5`
Vậy `x=5`
