Evaluating Logarithm

In this section, student will learn evaluating logarithm.
The word logarithm was coined from two Greek words"logos" which means a ratio and "arithmos" means numbers.
Logarithms and exponents are closely related to each other. The inverse of these operations gives us two distinct operations viz. extracting roots and taking logarithms.
a^m = b is exponential form.
It is read as mth power of 'a' is 'b'.
For each positive real number a, a≠ 1, the unique real number 'm' is called the logarithm of 'b' to the base 'a' or
log_ab = m if and only if a^m = b
'log' being the abbreviation of the word 'logarithm.

Properties of logarithm
1) log _a 1 = 0 because a ⁰ =1
2) log _a a = 1 because a ¹ =a
3) log _a a ^x = x because a ^x =a ^x

Evaluating logarithm

1) log ₃ 27
Solution : We know from definition that
log _a b = m, if and only if a ^m = b, a > 0 and a≠1
Let m = log ₃ 27
∴ 3 ^m = 27
3 ^m = 3 ³
∴ m = 3
so, log ₃ 27= 3

2) log ₂ √(32)
Solution : We know from definition that
log _a b = m, if and only if a ^m = b, a > 0 and a≠1
Let m = log ₂ √(32)
∴ 2 ^m = √(32)
2 ^m = (2 ⁵ ) ^1/2
2 ^m = 2 ^5/2
∴ m = 5/2
so, log ₂ √(32)= 5/2

Exponential to logarithmic form

27 = 128	⇒ log 2128 = 7
34 = 81	⇒ log 381 = 4
60 = 1	⇒ log 61 = 0
a-b = c	⇒ log ac = -b
43 = 64	⇒ log 4 64 = 3
72 = 49	⇒ log 7 49 = 2
53 = 125	⇒ log 5 125 = 3
103 = 1000	⇒ log 10 1000 = 3
83 = 512	⇒ log 8 512 = 3
15-2 = 1/225	⇒ log 15 (1/225) = -2

Logarithmic to Exponential form

log2 1 = 0	⇒ 20 = 1
log525 = 2	⇒ 52 = 25
log7343 = 3	⇒ 73 = 343
log10100 = 2	⇒ 102 = 100
log816 = 4/3	⇒ 84/3 = 16

11th grade math

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