Tolong bantu sekarang yah gan nomor 3

f(x) = (7logx) / (1 - 2 . 7logx)
f(7/x) = (7log(7/x)) / (1 - 2 . 7log(7/x))
= (7log7 - 7logx) / (1 - 2 (7log7 - 7logx))
= (1 - 7logx) / (1 - 2(1 - 7logx))
= (1 - 7logx) / (1 - 2 + 2. 7logx)
= (1 - 7logx) / (-1 + 2. 7logx) . (-1)/(-1)
= (7log x - 1) / (1 - 2 . 7logx)


f(7/x) + f(x) = (7logx - 1)/(1 - 2 . 7logx) + (7logx)/(1 - 2 7logx)
= (7logx - 1 + 7logx) / (1 - 2. 7logx)
= (-1 + 2 . 7logx) / -1(-1 + 2 . 7logx)
= -1

Cara cepat
Karena ini fungsi logaritma maka
f(7/x) + f(x) = f(7/x . x) = f(7) = (7log7) / (1 - 2 . 7log7) = 1/(1 - 2 . 1) = 1/-1 = -1