12) jika 5 log 4 = a dan 4 log 3 = b, nilai dari 13 log 20 =

⁵log 4 = a
⁴log 3 = b
¹²log 20 = ...?

Jwb:
¹²log 20 = ⁴log 20 / ⁴log 12
¹²log 20 = ⁴log 4×5 / ⁴log 3×4
¹²log 20 = (⁴log 4 + ⁴log 5) − (⁴log 3 + ⁴log 4)
¹²log 20 = (1 + 1/a) − (b + 1)
¹²log 20 = 1 − ab / a

Maaf jika salah ^^