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secondary 3 | E Maths
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Date Posted: 4 years ago
Views: 571
3^(z + 4) - 3^z = 80/81
3^z * 3^4 - 3^z = 80/81
3^z * 3^4 - 3^z * 1 = 80/81
3^z * (3^4 - 1) = 80/81
3^z * 80 = 80/81
3^z = 1/81
But 81 = 3^4 and 1/81 = 3^-4
so z = -4.
No need to use log for this question.
3^z * 3^4 - 3^z = 80/81
3^z * 3^4 - 3^z * 1 = 80/81
3^z * (3^4 - 1) = 80/81
3^z * 80 = 80/81
3^z = 1/81
But 81 = 3^4 and 1/81 = 3^-4
so z = -4.
No need to use log for this question.
See 1 Answer
3^(z+4) - 3^z
= 3^z * 3^4 - 3^z
= 81(3^z) - 1(3^z)
= 80(3^z)
= 3^z * 3^4 - 3^z
= 81(3^z) - 1(3^z)
= 80(3^z)
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