Question

Tinh gia tri cua cac bieu thuc sau voi /a/=1,5;b=-0,75

M= a+2ab-b

Answer 1

mk mới lp 6

Answer 2

\(\left|a\right|=1,5\Rightarrow\orbr{\begin{cases}a=1,5\\a=-1,5\end{cases}}\)

\(Th1:a=1,5;b=-0,75\)hay \(a=\frac{3}{2};b=\frac{-3}{4}\)

\(\Rightarrow M=\frac{3}{2}+2.\frac{3}{2}.\frac{-3}{4}-\frac{-3}{4}\)

\(=\frac{6}{4}+\frac{-9}{4}+\frac{3}{4}=0\)

\(Th2:a=-1,5;b=0,75\)hay \(a=\frac{-3}{2};b=\frac{-3}{4}\)

​\(\Rightarrow M=\frac{-3}{2}+2.\frac{-3}{2}.\frac{-3}{4}-\frac{-3}{4}\)​

\(=\frac{-6}{4}+\frac{9}{4}+\frac{3}{4}=\frac{3}{2}\)

Answer 3

Vì |a| = 1,5

\(\Rightarrow\orbr{\begin{cases}a=1,5\\a=-1,5\end{cases}}\)

Thay a;b vào M ta có :

\(\orbr{\begin{cases}M=1,5+2.\left(1,5\right).\left(-0,75\right)+0,75\\M=-1,5+2.\left(-1,5\right).\left(-0,75\right)+0,75\end{cases}}\)

\(\Rightarrow\orbr{\begin{cases}M=1,5+3.\frac{-3}{4}+0,75\\M=-1,5+2.\left(1,5\right).\left(0,75\right)+0,75\end{cases}}\)

\(\Rightarrow\orbr{\begin{cases}M=1,5-2,25+0,75\\M=-1,5+3.\frac{3}{4}+0,75\end{cases}}\)

\(\Rightarrow\orbr{\begin{cases}M=1,5-\left(2,25+0,75\right)\\M=-1,5+2,25+0,75\end{cases}}\)

\(\Rightarrow\orbr{\begin{cases}M=1,5-3\\M=-1,5+\left(2,25+0,75\right)\end{cases}}\)

\(\Rightarrow\orbr{\begin{cases}M=-1,5\\M=-1,5+3\end{cases}}\)

\(\Rightarrow\orbr{\begin{cases}M=-1,5\\M=1,5\end{cases}}\)

Vậy M = -1,5 hoặc M = 1,5