`y=2/5x`
`M` có tung độ là`(-2) => y =-2`
`=> -2=2/5x `
`=> x = -2 : 2/5 =-5`
Vậy `M` có hoành độ : `-5`
Câu 5
`2^x + 2^(x+1) + 2^(x+2) + 2^(x+3) = 120`
`<=> 2^x + 2^x *2 + 2^x *4 + 2^x * 8 = 120`
`<=>2^x ( 1+2+4+8) =120`
`<=> 2^x . 15 = 120`
`<=> 2^x = 120/15 = 8`
`<=> 2^x =2^3 `
`=>x=3`
b)\(\Rightarrow A=\dfrac{1-\dfrac{1}{7}+\dfrac{1}{49}-\dfrac{1}{343}}{\dfrac{8}{2}-\dfrac{4}{7}+\dfrac{4}{49}-\dfrac{4}{343}}=\dfrac{1-\dfrac{1}{7}+\dfrac{1}{49}-\dfrac{1}{343}}{4\left(1-\dfrac{1}{7}+\dfrac{1}{49}-\dfrac{1}{343}\right)}\)
\(A=\dfrac{1}{4}\)
Vậy `A=1/4`
\(2^x+2^{x+1}+2^{x+2}+2^{x+3}=120\)
\(\Leftrightarrow2^x\left(1+2+3+4\right)=20\)
\(\Leftrightarrow2^x.15=120\)
\(\Leftrightarrow2^x=8\Leftrightarrow x=3\)
\(A=\dfrac{1-\dfrac{1}{7}+\dfrac{1}{49}-\dfrac{1}{343}}{\dfrac{8}{2}-\dfrac{4}{7}+\dfrac{4}{49}-\dfrac{4}{343}}\)
\(=\dfrac{1-\dfrac{1}{7}+\dfrac{1}{49}-\dfrac{1}{343}}{4\left(1-\dfrac{1}{7}+\dfrac{1}{49}-\dfrac{1}{343}\right)}\)
\(=\dfrac{1}{4}\)
