Question

娜講

問這一題！

類題21
已知10*= 0.2,10"=20,試求:
(1) x-y=
(2) 2x-y=

Answer 1

qn

(1)
10ˣ⁻ʸ = 10ˣ / 10ʸ
= 0.2 / 20
= 0.01
= 10⁻²
x-y = -2

(2)
10²ˣ⁻ʸ = (10ˣ)² / 10ʸ
= (0.2)² / 20
= 0.002
= 2 × 10⁻³
2x-y = log(2 × 10⁻³)
= log2 - 3

qn

直接一點也可以
x = log(0.2) = log(2 × 10⁻¹) = log2 - 1
y = log(20) = log(2 × 10) = log2 + 1