Giải các phương trình sau:
a) 201 − x 99 + 203 − x 97 + 205 − x 95 + 3 = 0 ;
b) x 2 + x + 4 2 + x 2 + x + 7 3 = x 2 + x + 13 5 + x 2 + x + 16 6 Gợi ý: Bớt 3.
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a) \(\dfrac{x+1}{2004}+\dfrac{x+2}{2003}=\dfrac{x+3}{2002}+\dfrac{x+4}{2001}\)
⇔ \(\dfrac{x+1}{2004}+1+\dfrac{x+2}{2003}+1=\dfrac{x+3}{2002}+1+\dfrac{x+4}{2001}+1\)
⇔ \(\dfrac{x+2005}{2004}+\dfrac{x+2005}{2003}=\dfrac{x+2005}{2002}+\dfrac{x+2005}{2001}\)
⇔ \(\left(x+2005\right)\left(\dfrac{1}{2004}+\dfrac{1}{2003}-\dfrac{1}{2002}-\dfrac{1}{2001}\right)\)=0
Vì\(\left(\dfrac{1}{2004}+\dfrac{1}{2003}-\dfrac{1}{2002}-\dfrac{1}{2001}\right)\)<0 nên phương trinh đã cho tương đương:
x+2005=0 ⇔x=-2005
b) \(\dfrac{201-x}{99}+\dfrac{203-x}{97}+\dfrac{205-x}{95}+3=0\)
⇔ \(\dfrac{201-x}{99}+1+\dfrac{203-x}{97}+1+\dfrac{205-x}{95}+1=0\)
⇔ \(\dfrac{300-x}{99}+\dfrac{300-x}{97}+\dfrac{300-x}{95}=0\)
⇔ \(\left(300-x\right)\left(\dfrac{1}{99}+\dfrac{1}{97}+\dfrac{1}{95}\right)=0\)
Vì \(\left(\dfrac{1}{99}+\dfrac{1}{97}+\dfrac{1}{95}\right)>0\) nên phương trình đã cho tương đương:
300-x=0 ⇔ x=300
Sửa đề: \(\dfrac{201-x}{99}+\dfrac{203-x}{97}+\dfrac{205-x}{95}+3=0\)
Ta có: \(\dfrac{201-x}{99}+\dfrac{203-x}{97}+\dfrac{205-x}{95}+3=0\)
\(\Leftrightarrow\dfrac{201-x}{99}+1+\dfrac{203-x}{97}+1+\dfrac{205-x}{95}+1=0\)
\(\Leftrightarrow\dfrac{300-x}{99}+\dfrac{300-x}{97}+\dfrac{300-x}{95}=0\)
\(\Leftrightarrow\left(300-x\right)\left(\dfrac{1}{99}+\dfrac{1}{97}+\dfrac{1}{95}\right)=0\)
mà \(\dfrac{1}{99}+\dfrac{1}{97}+\dfrac{1}{95}>0\)
nên 300-x=0
hay x=300
Vậy:S={300}
Giải:
Ta có: \(\frac{201-x}{99}+\frac{205-x}{95}+\frac{203-x}{97}+3=0\)
\(\Leftrightarrow\frac{201-x}{99}+1+\frac{205-x}{95}+1+\frac{203-x}{97}+1=0\)
\(\Leftrightarrow\frac{300-x}{99}+\frac{300-x}{95}+\frac{300-x}{97}=0\)
\(\Leftrightarrow\left(300-x\right)\left(\frac{1}{99}+\frac{1}{95}+\frac{1}{97}\right)=0\)
\(\Leftrightarrow300-x=0\) (Vì \(\frac{1}{99}+\frac{1}{95}+\frac{1}{97}\ne0\))
\(\Leftrightarrow x=300\)
Vậy phương trình có nghiệm là \(x=300.\)
Chúc bạn học tốt@@
`(201-x)/99+(203-x)/97+(205-x)/95+3=0`
`<=>(201-x)/99+1+(203-x)/97+1+(205-x)/95+1=0`
`<=>(300-x)/99+(300-x)/97+(300-x)/95=0`
`<=>(300-x)(1/99+1/97+1/95)=0`
`<=>300-x=0`
`<=>x=300`
Vậy `x=300`
\(\Leftrightarrow\left(\dfrac{201-x}{99}+1\right)+\left(\dfrac{203-x}{97}+1\right)+\left(\dfrac{205-x}{95}+1\right)=0\)
=>300-x=0
=>x=300
<=> 300-x/99+300-x/97+300-x/95=0
<=>(300-x).(1/99+1/97+1/95)=0
<=>300-x=0
<=>x=300
✔
a ) x = 300
b) Gợi ý: Bớt 3 ở từng phân số. Đáp số: x = 1; x = -2