ĐK: \(-1\le x\le2\)Áp dụng BĐT: \(2ab\le a^2+b^2\)\(B=4\sqrt{\left(x+1\right)\left(2-x\right)}-1\)\(\le2\left(x+1+2-x\right)-1\)\(\le5\)\(B_{max}=5\Leftrightarrow x+1=2-x\Leftrightarrow x=\dfrac{1}{2}\left(tm\right)\)Câu trả lời: ĐK: \(-1\le x\le2\)Áp dụng BĐT: \(2ab\le a^2+b^2\)\(B=4\sqrt{\left(x+1\right)\left(2-x\right)}-1\)\(\le2\left(x+1+2-x\right)-1\)\(\le5\)\(B_{max}=5\Leftrightarrow x+1=2-x\Leftrightarrow x=\dfrac{1}{2}\left(tm\right)\)