對數函數 (10點)

1(a) 5^4 = 625 => x = 3

(b) log_a(3x + 5) = 2

log(3x + 5)/loga = 2

3x + 5 = a^2

x = (a^2 - 5)/3

2(a)(i) log_c15 = p + q

(ii) log_c 25 = 2q

(b) log_d 6 = 1/2

d^(1/2) = 6

d = 36

3 9log_5 x = 25log_x 5

9logx/log5 = 25log5/logx

(logx)^2 = (25/9)(log5)^2

logx = -(5/3)log5 or (5/3)log5

x = 5^(-5/3) or 5^(5/3)

2011-06-19 00:05:36 補充：
d^(1/2) = 6

d = 6^2

d = 36