Câu hỏi của Nguyễn Thanh Huyền

Question

Tìm x, biết :

a) 4x + 4x+1 = 80

b) 2x + 7 $\le$ 39

Hoàng Thị Ngọc Anh · Accepted Answer

a) $4^x+4^{x+1}=80$

$\Rightarrow4^x\left(1+4\right)=80$

$\Rightarrow4^x=80:5=16$

$\Rightarrow x=2$

b) $2^x+7\le39$

$\Rightarrow2^x\le32$

$\Rightarrow2^x\le2^5$

$\Rightarrow x\le5.$Câu trả lời: a) $4^x+4^{x+1}=80$

$\Rightarrow4^x\left(1+4\right)=80$

$\Rightarrow4^x=80:5=16$

$\Rightarrow x=2$

b) $2^x+7\le39$

$\Rightarrow2^x\le32$

$\Rightarrow2^x\le2^5$

$\Rightarrow x\le5.$

Nguyễn Thanh Hằng · Answer

a/ $4^x+4^{x+1}=80$

$\Leftrightarrow4^x\left(1+4\right)=80$

$\Leftrightarrow4^x.5=80$

$\Leftrightarrow4^x=16$

$\Leftrightarrow4^x=4^2$

$\Leftrightarrow x=2\left(tm\right)$

Vậy ...

b/ $2^x+7\le39$

$\Leftrightarrow2^x\le32$

$\Leftrightarrow2^x\le2^5$

$\Leftrightarrow x\le5$

$\Leftrightarrow x\in\left\{0;1;2;3;4;5\right\}$

Vậy ..Câu trả lời: a/ $4^x+4^{x+1}=80$