\(a.A=48-y^2-2y=-\left(y^2+2y+1\right)+49=-\left(y+1\right)^2+49\text{≥}49\) ⇒ \(A_{Max}=49."="\) ⇔ \(y=-1\)
\(b.B=4x^2-12x+17=4x^2-12x+9+8=\left(2x-3\right)^2+8\text{≥}8\)
⇒ \(B_{MIN}=8."="\) ⇔ \(x=\dfrac{3}{2}\)
a) \(A=48-y^2-2y\)
.........= \(-\left(y^2+2y+1+47\right)\)
.........= \(-\left[\left(y+1\right)^2+47\right]\)
.........= \(-\left(y+1\right)^2-47\le-47,\forall x\)
Vì: \(\left(y+1\right)^2\ge0,\forall x\)
Dấu "=" xảy ra <=> y + 1 = 0
.........................<=> y = - 1
Vậy Max A = - 47 <=> y = -1