Monday, April 16, 2018

Algebra 2 Problems of the Day

Algebra 2 is not my usual subject, but I do get asked about the problems occasionally. So I've decided to run a couple of Regents problems daily for a while. If there's a positive reaction (or at least, a lack of negative reaction), I may continue it.

More Algebra 2 problems.

January 2018
13. If aebt = c, where a, b, and c are positive, then t equals

Answer: (3) ln(c/a) / b
You start with: aebt = c
Divide both sides by a: ebt = c/a
Take the natural log: ln(ebt) = ln(c/a)
which gives you: bt = ln(c/a)
Divide by b: t = ln(c/a) / b.

14. For which values of x, rounded to the nearest hundredth, will |x2 - 9| - 3 = log3x?

(1) 2.29 and 3.63
(2) 2.37 and 3.54
(3) 2.84 and 3.17
(4) 2.92 and 3.06

Answer: (1) 2.29 and 3.63
If you graph the system: y = |x2 - 9| - 3 and y = log(x)/log(3), you can use the intersection function the points of intersection (2.29, 0.754) and (3.63, 1.173).
Use (2nd)(CALC), option (5)Intersect and hit ENTER three times.
Or you can graph log(x)/log(3) - |x2 - 9| + 3, and look for the zeroes.
Use (2nd)(CALC), option (2)Zero.

Given that this is a multiple choice question, you could also use a list of information and enter that last equation into the calculator to see which gives you zero -- or very close to zero, because we have approximate answers. Be careful, though, because there's a lot of information to enter and typos happen.

Comments and questions welcome.


Grace A said...

Why do we have divide logx by log3

(x, why?) said...

If you're calculator lets you enter log base 3, then you don't have to.

If you have an older operating system, like mine, you have to convert it to put it into the calculator.

Here's a MathBits page with more information:

Grace A said...

Thank you !