Question

\(A=\sqrt{4x+20}-2\sqrt{x+5}+\sqrt{9x+45}\) 

a) Rút gọn A

b) Tìm x để A=6

Answer 1

\(a,ĐK:x\ge-5\\ A=2\sqrt{x+5}-2\sqrt{x+5}+3\sqrt{x+5}=3\sqrt{x+5}\\ b,A=6\Leftrightarrow\sqrt{x+5}=\dfrac{6}{3}=2\\ \Leftrightarrow x+5=4\\ \Leftrightarrow x=-1\left(tm\right)\)

Answer 2

\(A=2\sqrt{x+5}-2\sqrt{x+5}+3\sqrt{x+5}\)

\(A=3\sqrt{x+5}\)

\(3\sqrt{x+5}=6\)

\(\sqrt{x+5}=2\)

\(\left\{{}\begin{matrix}2\ge0\left(ld\right)\\x+5=4\end{matrix}\right.\)

\(x=-1\)