a, Ta có: \(-x^2+4x-9+5=-x^2+4x-4\)
\(=-\left(x^2-4x+4\right)\)
\(=-\left(x-2\right)^2\le0\)
=> \(-x^2+4x-9\le-5\)
b, Ta có: \(x^2-2x+9-8=x^2-2x+1=\left(x-1\right)^2\ge0\)
=> \(x^2-2x+9\ge8\)
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a, Ta có: −x2+4x−9+5=−x2+4x−4−x2+4x−9+5=−x2+4x−4
=−(x2−4x+4)=−(x2−4x+4)
=−(x−2)2≤0=−(x−2)2≤0
=> −x2+4x−9≤−5−x2+4x−9≤−5
b, Ta có: x2−2x+9−8=x2−2x+1=(x−1)2≥0x2−2x+9−8=x2−2x+1=(x−1)2≥0
=> x2−2x+9≥8
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