Question

1. voi gt nao cua bien x da thuc nhom co gia tri lon nhat

a B= 4x - xmu2 +1

b C= (1-x).(x+2).(x+3).(x+6)

Answer 1

A) gtln B =5 khi x =2

Answer 2

\(\Leftrightarrow B=-\left(x^2-4x-1\right)\)

\(\Leftrightarrow B=-\left(x^2-4x+4-5\right)\)

\(\Leftrightarrow B=-\left(x-2\right)^2+5\)

Ta có \(\left(x-2\right)^2\ge0\)với mọi x

  \(\Leftrightarrow-\left(x-2\right)^2\le0\)

\(\Leftrightarrow-\left(x-2\right)^2+5\le0+5\)

hay               \(B\)            \(\le5\)

Dấu "=" xảy ra khi \(\left(x-2\right)^2=0\)

                     .  \(\Leftrightarrow x-2\)\(=0\)

                       \(\Leftrightarrow\)\(x\)      \(=2\)

Vậy min B=5 tại x=2

Answer 3

lam cau b ay ban cau a minh lam roi