McGraw Hill Glencoe Algebra 2, 2012
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McGraw Hill Glencoe Algebra 2, 2012 View details
6. Common Logarithms
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Exercise 31 Page 496

{ y | y ≥ - 3.8188 }

Practice makes perfect

To solve the given exponential inequality, we will use the Inequality Property of Logarithmic Functions.

Inequality Property of Logarithmic Functions

&Ifb > 1, log_b x > log_b y if and only if x > y. &Ifb > 1, log_b x < log_b y if and only if x < y.

Using this property, we can rewrite the exponential inequality as a logarithmic inequality. 3^(y-1) ≤ 4^y ⇔ log 3^(y-1) ≤ log 4^yTo solve the above logarithmic inequality, we need to recall the Power Property of Logarithms.

Power Property of Logarithms

log_b m^p = p log_b m, where m and b are positive numbers, with b≠ 1.

Let's use it and solve the inequality!

log 3^(y-1) ≤ log 4^y

log_()(a^m)= m* log_()(a)

(y-1)log 3 ≤ y log 4
y log 3 - log 3 ≤ y log 4
- log 3 ≤ y log 4 - y log 3
- log 3 ≤ y (log 4 - log 3)

The final step to isolate y will be to divide both sides of the inequality by log 4 - log 3. Before we take this step, let's stop for a moment and think about the sign of the expression. 4>3 ⇔ log 4 > log 3 Because log 4 is greater than log 3, we know that the difference between log 4 and log 3 will be a positive number. Therefore, to divide by this value, we mustn't reverse the inequality sign.

- log 3 ≤ y (log 4 - log 3)
- log 3/log 4 - log 3 ≤ y
- 3.8188 ≤ y
y ≥ - 3.8188

Finally, we can write our answer in set-builder notation. { y | y ≥ - 3.8188 }