Tìm số nguyên x biết : x/4 =18/x+1

2 câu trả lời

x4=18x+1

x.(x+1)4.(x+1)=18.4(x+1).4

x2+x=72

x2+x-72=0

x2+9x-8x-72=0

x(x-8)+9.(x-9)=0

(x+9).(x-8)=0

[x+9=0x8=0 

[x=9x=8 

Vậy x{-9;8}

 

x4=18x+1

x.(x+1)=18.4

x2+x=72

x2+x-72=0

x2+9x-8x-72=0

x(x+9)-8(x+9)=0

(x-8)(x+9)=0

x-8=0            hoặc               x+9=0

x=8                 hoặc               x=-9

Vậy x∈{8;-9}