`a,` `9y^2-36=0`
`⇒9y^2=36`
`⇒y^2=4`
`⇒y=±2`
`b,` `(x-1).(x+1).(x^2+1/2)=0`
\(⇒\left[ \begin{array}{l}x-1=0\\x+1=0\\x^2+\dfrac12=0\end{array} \right.\)
\(⇒\left[ \begin{array}{l}x=1\\x=-1\\x^2=-\dfrac12 (KTM)\end{array} \right.\)
`c,` `|x-2+4|=0`
`⇒x+2=0`
`⇒x=-2`
`d,` `|x-3|+5-x=0` `(1)`
Nếu `x-3≥0⇒x≥3`
`⇒(1)` có dạng : `x-3+5-x=0`
`⇒2=0` `(`vô lý`)`
Nếu `x-3<0⇒x<3`
`⇒(1)` có dạng : `3-x+5-x=0`
`⇒8-2x=0`
`⇒x=4` `(KTM)`
`⇒x∈`$\varnothing$
