a: \(=4a^2+4a+1-6=\left(2a+1\right)^2-6>=-6\)
Dấu = xảy ra khi a=-1/2
b: \(=-\left(y^2-4y-3\right)\)
\(=-\left(y^2-4y+4-7\right)\)
\(=-\left(y-2\right)^2+7< =7\)
Dấu = xảy ra khi y=2
c: \(=-25x^2+3x\)
\(=-25\left(x^2-\dfrac{3}{25}x\right)\)
\(=-25\left(x^2-2\cdot x\cdot\dfrac{3}{50}+\dfrac{9}{2500}-\dfrac{9}{2500}\right)\)
\(=-25\left(x-\dfrac{3}{50}\right)^2+\dfrac{9}{100}< =\dfrac{9}{100}\)
Dấu = xảy ra khi x=3/50
e: \(=3\left(x^2+\dfrac{7}{3}x+\dfrac{1}{3}\right)\)
\(=3\left(x^2+2\cdot x\cdot\dfrac{7}{6}+\dfrac{49}{36}-\dfrac{37}{36}\right)\)
\(=3\left(x+\dfrac{7}{6}\right)^2-\dfrac{37}{12}>=-\dfrac{37}{12}\)
Dấu = xảy ra khi x=-7/6
