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Mathematics

By converting to exponential form, find the value of each of the following:

(i) log2 64

(ii) log8 32

(iii) log3 19\dfrac{1}{9}

(iv) log0.5 (16)

(v) log2 (0.125)

(vi) log7 7

Logarithms

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Answer

(i) Let,

⇒ log2 64 = x

⇒ 64 = 2x

⇒ 26 = (2)x

Equating the exponents,

⇒ x = 6

Hence, log2 64 = 6.

(ii) Let,

⇒ log8 32 = x

⇒ 32 = 8x

⇒ 25 = (23)x

⇒ 25 = (2)3x

Equating the exponents,

⇒ 3x = 5

⇒ x = 53\dfrac{5}{3}.

Hence, log8 32 = 53\dfrac{5}{3}.

(iii) Let,

log3 19=x19=3x132=3x32=3x\Rightarrow \log_{3} \space {\dfrac{1}{9}} = x \\[1em] \Rightarrow \dfrac{1}{9} = 3^x \\[1em] \Rightarrow \dfrac{1}{3^2} = 3^x \\[1em] \Rightarrow 3^{-2} = 3^x \\[1em]

Equating the exponents,

⇒ x = -2.

Hence, log3 19\log_{3} \space {\dfrac{1}{9}} = -2.

(iv) Let,

⇒ log0.5 (16) = x

⇒ 16 = 0.5x

⇒ 24 = (12)x\Big(\dfrac{1}{2}\Big)^x

⇒ 24 = (2-1)x

⇒ 24 = (2)-x

Equating the exponents,

⇒ -x = 4

⇒ x = -4.

Hence, log0.5 (16) = -4.

(v) Let,

⇒ log2 (0.125) = x

⇒ 0.125 = 2x

1251000\dfrac{125}{1000} = 2x

18\dfrac{1}{8} = 2x

123\dfrac{1}{2^3} = 2x

⇒ 2-3 = 2x

Equating the exponents,

⇒ x = -3.

Hence, log2 (0.125) = -3.

(vi) Let,

⇒ log7 7 = x

⇒ 7 = 7x

⇒ 71 = 7x

Equating the exponents,

⇒ x = 1.

Hence, log7 7 = 1.

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