How do I change base for Logarithms on a TI-30xIIS calculator?

Log a (b) = log (b)/log(a).

The common log (base 10) and the natural log (base e) have dedicated keys.

If you need another base calculated, use the change of bases rule.

For example:

log₂8 = log(8) / log(2)

You can use either log or ln:

log₂32 = ln(32) / ln(2)

There doesn't appear to be any key stroke function to do that operation. You'll have to find the logarithm of the object and then divide by the logarithm of the desired base. You can use either natural or common logs for the operations as long as you are consistent.

To find the log of a to base b:

log_b(a) = log(a)/log(b) = ln(a)/ln(b)

if all else fails, use the change of base formula