Inequalities af(x)>ag(x)
If a>1, at increases in t, so af>ag ⇔ f>g (on the common domain of the inequality).
If 0<a<1, the exponential decreases, so af>ag ⇔ f<g.
If the bases differ, you usually take logarithms or match bases; with ln the inequality sign is unchanged (ln is increasing), but both sides must be positive.
First ensure a>0, a=1, and write the domain for f,g
How the sign transfers
| Base | From af>ag you get |
|---|---|
| a>1 | f>g |
| 0<a<1 | f<g |
After reducing to f(x)>g(x), intersect with the domain on the number line.
Example “interval” style answer
(3;+∞]
💡Next lesson — the formal definition of the logarithm and the basic logarithmic identity.
✅You transfer the inequality between af and f, g according to a>1 or 0<a<1.