SOLUTION: Please help me solve this question Solve the system; logx base a.log ( xyz ) base a = 48 Logy base a.log ( xyz ) base a = 12, a > 0, a is not = to 1

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Question 1034317: Please help me solve this question
Solve the system; logx base a.log ( xyz ) base a = 48
Logy base a.log ( xyz ) base a = 12, a > 0, a is not = to 1
Logz base a.log ( xyz ) base a = 84

Answer by ikleyn(52781) About Me  (Show Source):
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Please help me solve this question
Solve the system; logx base a.log ( xyz ) base a = 48,
Logy base a.log ( xyz ) base a = 12,
Logz base a.log ( xyz ) base a = 84,
a > 0, a is not = to 1
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log%28a%2C%28x%29%29%2Alog%28a%2C+%28xyz%29%29 = 48,   (1)
log%28a%2C%28y%29%29%2Alog%28a%2C+%28xyz%29%29 = 12,   (2)
log%28a%2C%28z%29%29%2Alog%28a%2C+%28xyz%29%29 = 84.   (3)

Add (1), (2) and (3) (both sides). You will get

%28log%28a%2C+%28xyz%29%29%29%5E2 = 48 + 12 + 84 = 144.

Hence, log%28a%2C+%28xyz%29%29 = +/- 12.

Now, consider two cases.

a) log%28a%2C+%28xyz%29%29 = + 12.

   Then log%28a%2C%28x%29%29 = 48%2F12 = 4  --->  x = a%5E4,
        log%28a%2C%28y%29%29 = 12%2F12 = 1  --->  y = a,
        log%28a%2C%28z%29%29 = 84%2F12 = 7  --->  z = a%5E7.

b) log%28a%2C+%28xyz%29%29 = - 12.

   Then log%28a%2C%28x%29%29 = -48%2F12 = -4  --->  x = a%5E%28-4%29,
        log%28a%2C%28y%29%29 = -12%2F12 = -1  --->  y = a%5E%28-1%29,
        log%28a%2C%28z%29%29 = -84%2F12 = -7  --->  z = a%5E%28-7%29.

Thus you have two solutions (or two sets of solutions).