Hi,
I'm have trouble with this particular question:
0.2^x = 15
Can anybody help please with a full explanation of how they got there?
2007-12-01 06:30:56 · 2 answers · asked by Anonymous in Science & Mathematics ➔ Mathematics
Please don't include logarithms! I haven't done those yet.
I worked out the answer to be -3 which seems right, however, I can't seem to find my method! I only did it by trial and error!
2007-12-01 06:43:34 · update #1
0.2 ^ x = 15
Take logarithm
x log 0.2 = log 15
x = log 15 / log 0.2
log 15 = 1.17609126
log 0.2 = -0.698970004
x = 1.17609126/-0.698970004 = -1.6826
2007-12-01 06:37:37 · answer #1 · answered by A Little Sarcasm Helps 5 · 0⤊ 0⤋
Take the logarithm of both sides.
x log 0.2 = log 15
So x = log 15/log 0.2
But 0.2 = 1/5
and log(1/5) = log 1 - log 5 = -log 5.
So the answer is -log 15/ log 5 = -1.682(approx)
Note: All logs here are natural logs.
Another way to proceed:
0.2 = 1/5
and (1/5)^x = 5 ^(-x).
The rest is the same as before.
2007-12-01 14:42:54 · answer #2 · answered by steiner1745 7 · 0⤊ 0⤋