Đáp án:
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`a,`
`x^2=9`
`↔` \(\left[ \begin{array}{l}x^2=3^2\\x^2=(-3)^2\end{array} \right.\)
`↔` \(\left[ \begin{array}{l}x=3\\x=-3\end{array} \right.\)
Vậy `x=3` hoặc `x=-3`
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`b,`
`x^2+5=9`
`↔x^2=9-5`
`↔x^2=4`
`↔` \(\left[ \begin{array}{l}x^2=2^2\\x^2=(-2)^2\end{array} \right.\)
`↔` \(\left[ \begin{array}{l}x=2\\x=-2\end{array} \right.\)
Vậy `x=2` hoặc `x=-2`
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`c,`
`x^2-6=10`
`↔x^2=10+6`
`↔x^2=16`
`↔` \(\left[ \begin{array}{l}x^2=4^2\\x^2=(-4)^2\end{array} \right.\)
`↔` \(\left[ \begin{array}{l}x=4\\x=-4\end{array} \right.\)
Vậy `x=4` hoặc `x=-4`
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`d,`
`5×x^2=45`
`↔ x^2=45÷5`
`↔x^2=9`
`↔` \(\left[ \begin{array}{l}x^2=3^2\\x^2=(-3)^2\end{array} \right.\)
`↔` \(\left[ \begin{array}{l}x=3\\x=-3\end{array} \right.\)
Vậy `x=3` hoặc `x=-3`
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`e,`
`2x^2 +5=23`
`↔ 2x^2=23-5`
`↔2x^2=18`
`↔x^2=18÷2`
`↔x^2=9`
`↔` \(\left[ \begin{array}{l}x^2=3^2\\x^2=(-3)^2\end{array} \right.\)
`↔` \(\left[ \begin{array}{l}x=3\\x=-3\end{array} \right.\)
Vậy `x=3` hoặc `x=-3`
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`f,`
`3x^2 -4=71`
`↔3x^2=71+4`
`↔3x^2=75`
`↔x^2=75÷3`
`↔x^2=25`
`↔` \(\left[ \begin{array}{l}x^2=5^2\\x^2=(-5)^2\end{array} \right.\)
`↔` \(\left[ \begin{array}{l}x=5\\x=-5\end{array} \right.\)
Vậy `x=5` hoặc `x=-5`
