Đáp án:
`S={5/2;-5/2}`
`S={1/3;-1/3}`
`S={0;3;-3}`
`S={-1/2}`
Giải thích các bước giải:
`25-4x^2=0`
`<=>5^2-(2x)^2=0`
`<=>(5-2x)(5+2x)=0`
`<=>[(5-2x=0),(5+2x=0):}`
`<=>`\(\left[ \begin{array}{l}x=\dfrac{5}{2}\\x=-\dfrac{5}{2}\end{array} \right.\)
Vậy `S={5/2;-5/2}`
`9x^2-1=0`
`<=>(3x)^2-1^2=0`
`<=>(3x-1)(3x+1)=0`
`<=>[(3x-1=0),(3x+1=0):}`
`<=>`\(\left[ \begin{array}{l}x=\dfrac{1}{3}\\x=-\dfrac{1}{3}\end{array} \right.\)
Vậy `S={1/3;-1/3}`
`x^3-9x=0`
`<=>x(x^2-9)=0`
`<=>x(x-3)(x+3)=0`
`<=>[(x=0),(x-3=0),(x+3=0):}`
`<=>[(x=0),(x=3),(x=-3):}`
Vậy `S={0;3;-3}`
`x^2+x+1/4=0`
`<=>x^2+2*x*1/2+(1/2)^2=0`
`<=>(x+1/2)^2=0`
`<=>x+1/2=0<=>x=-1/2`
Vậy `S={-1/2}`.
