Question

Bài 1: Tìm x trong các tỉ lệ thức sau

a) x/0,9 = 5/6

b) 16 : x^2 = x : (-4)

c) x/2 = 8/x

d) x-1/x+2 = x+2/x+3

Answer 1

a)x/0,9=5/6 =>6x=5.0,9=4,5

=>x=4,5/6=0,75

b)16/x²=x/-4 =>16.(-4)=x³ =>x³=-64=(-4)³ =>x=-4

c)x/2=8/x =>x²=2.8=16 => x=+-4

d)x-1/x+2=x+2/x+3 =>(x+2)(x+2)=(x-1)(x+3)

=>x²+4x+4=x²+2x-3

=>x²-x²+4x-2x+4+3=0

=>2x+7=0

=>2x=-7 =>x=-7/2=-3,5

Answer 2

a) có \(\dfrac{x}{0,9}=\dfrac{5}{6}\)

x.6=5.0,9

x.6=\(\dfrac{9}{2}\)

x=\(\dfrac{9}{2}:6\)

x=\(\dfrac{9}{2}.\dfrac{1}{6}\)

x=\(\dfrac{3}{4}\)

b) \(\dfrac{16}{x^2}=\dfrac{x}{-4}\)

16.(-4)=\(x^3\)

-64=\(x^3\)

Mà 64=(-4)^3

Suy ra x=-4

c)\(\dfrac{x}{2}=\dfrac{8}{x}\)

x.x=8.2

\(x^2\) =16

Suy ra x=4 hoặc x=-4

d) \(\dfrac{x-1}{x+2}=\dfrac{x+2}{x+3}\)

(x-1)(x+3)=(x+2)(x+2)

\(x^2+3x-x-3=x^2+2x+2x+4\)

\(x^2-4x-3=x^2+4x+4\)

8x=-7

x=-7/8