15.(x-4)=45 x-10=-65 -125+(x+125)=-25 2.2^x=2^8

Đáp án + Giải thích các bước giải:

$\text{a/ 15. (x - 4) = 45}$ $\\$ $\text{x - 4 = 45 : 15}$ $\\$ $\text{x - 4 = 3}$ $\\$ $\text{x = 3 + 4}$ $\\$ $\text{x = 7}$ $\\$ $\text{b/ -125 + (x + 125) = -25}$ $\\$ $\text{-125 + x + 125 = -25}$ $\\$ $\text{(-125 + 125) + x = -25}$ $\\$ $\text{x = -25}$ $\\$ $\text{c/ 2. $2^{x}$ = $2^{8}$}$ $\\$ $\text{$2^{x}$ = $2^{8}$ : 2}$ $\\$ $\text{$2^{x}$ = $2^{7}$}$ $\\$ $\text{⇒ x = 7}$