Toán Lớp 8: Tìm x
a) 16x^2 – 1 = 0
b) x^2 + 1/4 = 0
c) x^3 + 3x^2 – ( x + 3) = 0
Leave a reply
Register Now
Login
Lost Password
Lost your password? Please enter your email address. You will receive a link and will create a new password via email.
Toán Lớp 8: Tìm x
a) 16x^2 – 1 = 0
b) x^2 + 1/4 = 0
c) x^3 + 3x^2 – ( x + 3) = 0
Comments ( 2 )
16x^2-1=0
<=>16x^2=0+1
<=>16x^2=1
<=>x^2=1:16
<=>x^2=1/16
<=>x^2=(+-1/4)^2
<=>x=+-1/4
Vậy x=+-1/4
b)
x^2+1/4=0
Ta có:
x^2ge0forallx
=>x^2+1/4ge1/4>0
=> Vô nghiệm
Vậy không có giá trị của x thỏa mãn
c)
x^3+3x^2-(x+3)=0
<=>x^2.(x+3)-(x+3)=0
<=>(x^2-1)(x+3)=0
<=>(x-1)(x+1)(x+3)=0
<=>[(x-1=0),(x+1=0),(x+3=0):}
<=>[(x=1),(x=-1),(x=-3):}
Vậy x\in{1;-1;-3}