12) zpět

9 – 2^x = 2^{3 – x}

9 – 2^x =

9 · 2^x – (2^x)² = 8

substituce: 2^x = y

-y² + 9y – 8 = 0

y² – 9y + 8 = 0

(y – 1)(y – 8) = 0

y₁ = 1 » 2^x = 1

x₁ = 0

y² = 8 » 2^x = 8

x₂ = 3