Toán Cho tam thức bậc hai ã^2+bx+c,tìm gtnn nếu a>0,tìm gtln nếu a<0 14/09/2021 By Liliana Cho tam thức bậc hai ã^2+bx+c,tìm gtnn nếu a>0,tìm gtln nếu a<0
\[a{x^2} + bx + c = a({x^2} + 2*\frac{b}{{2a}}x + \frac{{{b^2}}}{{4{a^2}}}) – \frac{{{b^2}}}{{4a}} + c = a{(x + \frac{b}{{2a}})^2} + \frac{{ – {b^2} + 4ac}}{{4a}}\] Nếu a>0 thì min=\[\frac{{ – {b^2} + 4ac}}{{4a}}\] Nếu a<0 thì max=\[\frac{{ - {b^2} + 4ac}}{{4a}}\] Trả lời
\[a{x^2} + bx + c = a({x^2} + 2*\frac{b}{{2a}}x + \frac{{{b^2}}}{{4{a^2}}}) – \frac{{{b^2}}}{{4a}} + c = a{(x + \frac{b}{{2a}})^2} + \frac{{ – {b^2} + 4ac}}{{4a}}\]
Nếu a>0 thì min=\[\frac{{ – {b^2} + 4ac}}{{4a}}\]
Nếu a<0 thì max=\[\frac{{ - {b^2} + 4ac}}{{4a}}\]