Question

Cho ham so (P): y= x²+ bx+c co GTNN la 4 va do thi (P) di qua diem A(0;5), khi do gia tri cua b,c la

Answer 1

Lời giải:

$A\in (P)\Rightarrow 5=0^2+b.0+c=c$

$y=x^2+bx+c=x^2+bx+5=(x+\frac{b}{2})^2+5-\frac{b^2}{4}\geq 5-\frac{b^2}{4}$

$\Rightarrow y_{\min}=5-\frac{b^2}{4}=4$

$\Rightarrow b^2=4\Rightarrow b=\pm 2$

Vậy $b=\pm 2; c=5$