Đáp án `+` Giải thích các bước giải:

 ` a) 2(x+1)^2 - 28 = 100 `

` <=> 2(x+1)^2 = 128 `

` <=> (x+1)^2 = 64 `

` <=> (x+1)^2 = 8^2 `

TH1:

` x+1 = 8 `

` <=> x = 8-1 `

` <=> x = 7 `

TH2:

` x + 1 = -8 `

` <=> x = (-8) - 1 `

` <=> x = -9 `

Vậy: ` x ∈ {7; -9} `

____________________________

` b) 3^2 x + 1 = 81 `

` <=> 9x = 81 - 1 `

` <=> 9 x = 80 `

` <=> x = 80 : 9 `

` <=> x = 80/9 `

Vậy: ` x = 80/9 `

____________________________

` c) 3^x + 3^{x+2} = 810 `

` <=> 3^x + 3^x . 3^2 = 810 `

` <=> 3^x . (1 + 3^2) = 810 `

` <=> 3^x . 10 = 810 `

` <=> 3^x = 81 `

` <=> 3^x = 3^4 `

` <=> x = 4 `

Vậy: ` x = 4 `

____________________________

` d) 2^3 . 2^x - 2,1 = 13,9 `

` <=> 2^{3+x} = 16 `

` <=> 2^{3+x} = 2^4 `

` <=> 3 + x = 4 `

` <=> x = 1 `

Vậy: ` x = 1 `

____________________________

` e) 2^x + 2^{x+4} = 544 `

` <=> 2^x + 2^x . 2^4 = 544 `

` <=> 2^x . (1 + 2^4) = 544 `

` <=> 2^x . 17 = 544 `

` <=> 2^x = 32 `

` <=> 2^x = 2^5 `

` <=> x = 5 `

Vậy: ` x = 5 `

` tt (@NgManh06) `