Wednesday, December 7, 2011

12-5 notes - Change of base and graphing calculator

p128, item 20, explain how to evaluate the expression using a graphing calculator.

f(x) = 3 log base 2 (x + 4) - 2

The inside expression is logarithm base 2 of ( x + 4 ).  There is no log base 2 key on the calculator, so we need to change the base to 10 so we can use the LOG key.

To change a log expression's base, rewrite the log expression with the new base you want to use.

log base 10 (x + 4) 

Divide by the log in the new base of (the number that is the old base)

log base 2 (x + 4) = log base 10 (x + 4)    
                           log base 10 (2)

To finish the problem, use this quotient in a calculator key sequence with the 3 in front and the -2 in back.

y= 3 ( (log (X + 4) divided by log (2)) - 2
enter, trace



No comments:

Post a Comment