Chapter 8

9. The loudness, L, of a sound in decibels (dB) can be calculated using
A
the formula L 5 10 log Q I R , where I is the intensity of the sound
I0
in watts per square metre (W>m 2 ) and I 0 5 10 212 W>m 2 .
a) A teacher is speaking to a class. Determine the intensity of the
teacher’s voice if the sound level is 50 dB.
b) Determine the intensity of the music in the earpiece of an MP3
player if the sound level is 84 dB.
10. Solve log a (x 1 2) 1 log a (x 2 1) 5 log a (8 2 2x) .
T
11. Use graphing technology to solve each equation to two decimal
places.
a) log (x 1 3) 5 log (7 2 4x) c) 2 log x 5 1
b) 5 x 5 3 x11 d) log (4x) 5 log (x 1 1)
12. Solve log 5 (x 2 1) 1 log 5 (x 2 2) 2 log 5 (x 1 6) 5 0.
13. Explain why there are no solutions to the equations log 3 (28) 5 x
and log 23 9 5 x.
14. a) Without solving the equation, state the restrictions on the
variable x in the following: log (2x 2 5) 2 log (x 2 3) 5 5
b) Why do these restrictions exist?
15. If log Q x 1 y
where x . 0, y . 0,
5 R 5 1 (log x 1 log y),
2
show that x 2 1 y 2 5 23xy.
log (35 2 x
16. Solve
3 )
5 3.
log (5 2 x)
17. Given log 2 a 1 log 2 b 5 4, calculate all the possible integer values
C
of a and b. Explain your reasoning.
Extending
18. Solve the following system of equations algebraically.
y 5 log 2 (5x 1 4)
y 5 3 1 log 2 (x 2 1)
19. Solve each equation.
a) log 5 (log 3 x) 5 0 b)
log 2 (log 4 x) 5 1
20. If Q1 and log x2y 8 523 , calculate the values of x and y.
2 Rx1y 5 16
492
8.6 Solving Logarithmic Equations
NEL