Đáp án:
`a)`
`x^2+16x+64=0`
`<=>x^2+2.8.x+8^2=0`
`<=>(x+8)^2=0`
`<=>x+8=0`
`<=>x=-8`
Vậy `x=-8`
`b)`
`4-4x+x^2=0`
`<=>x^2-2.x.2+2^2=0`
`<=>(x-2)^2=0`
`<=>x-2=0`
`<=>x=2`
Vậy `x=2`
`c)`
`25x^2+10x+1=0`
`<=>(5x)^2+2.5x.1+1^2=0`
`<=>(5x+1)^2=0`
`<=>5x+1=0`
`<=>5x=-1`
`<=>x=-1/5`
Vậy `x=-1/5`
`d)`
`x^2+14x+49=0`
`<=>x^2+2.7.x+7^2=0`
`<=>(x+7)^2=0`
`<=>x+7=0`
`<=>x=-7`
Vậy `x=-7`
`e)`
`-5+20x+25x^2=-9`
`<=>25x^2+20x-5+9=0`
`<=>25x^2+20x+4=0`
`<=>(5x)^2+2.5x.2+2^2=0`
`<=>(5x+2)^2=0`
`<=>5x+2=0`
`<=>5x=-2`
`<=>x=-2/5`
`g)`
`16x^2+8x+1=36`
`<=>16x^2+8x+1-36=0`
`<=>16x^2+8x-35=0`
`<=>16x^2+28x-20x-35=0`
`<=>4x(4x+7)-5(4x+7)=0`
`<=>(4x+7).(4x-5)=0`
`<=>`\(\left[ \begin{array}{l}4x+7=0\\4x-5=0\end{array} \right.\)
`<=>`\(\left[ \begin{array}{l}4x=-7\\4x=5\end{array} \right.\)
`<=>`\(\left[ \begin{array}{l}x=\dfrac{-7}{5}\\x=\dfrac{5}{4}\end{array} \right.\)
Vậy `x∈{5/4;-7/4}`
