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Mathematics

Given log10 x = 2a and log10 y = b2\dfrac{b}{2}.

(i) Write 10a in terms of x.

(ii) Write 102b + 1 in terms of y.

(iii) If log10P = 3a - 2b, express P in terms of x and y.

Logarithms

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Answer

(i) Given,

⇒ log10 x = 2a

⇒ x = 102a

⇒ x = (10a)2

Taking square root on both sides, we get :

x=10a\Rightarrow \sqrt{x} = 10^a

Hence, 10a = x\sqrt{x}.

(ii) Given,

⇒ 102b + 1

⇒ 102b.101 ………(1)

Given,

log10y=b2y=10b2y4=(10b2)4y4=102b ……(2)\Rightarrow \text{log}_{10}y = \dfrac{b}{2} \\[1em] \Rightarrow y = 10^{\dfrac{b}{2}} \\[1em] \Rightarrow y^4 = (10^{\dfrac{b}{2}})^{4} \\[1em] \Rightarrow y^4 = 10^{2b} \text{ ……(2)}

Substituting value of 102b from equation (2) in equation (1), we get :

⇒ y4.101

⇒ 10y4.

Hence, 102b + 1 = 10y4.

(iii) Given,

⇒ log10 P = 3a - 2b

⇒ P = 103a - 2b

⇒ P = 103a.10-2b

⇒ P = 103a102b\dfrac{10^{3a}}{10^{2b}}

We know that: (shown above)

y4 = 102b

and

x\sqrt{x} = 10a

∴ P = 103a102b\dfrac{10^{3a}}{10^{2b}} = (10a)3y4=(x)3y4=x32y4\dfrac{(10^{a})^3}{y^4} = \dfrac{(\sqrt{x})^3}{y^4} = \dfrac{x^{\dfrac{3}{2}}}{y^4}.

Hence, P = x32y4\dfrac{x^{\dfrac{3}{2}}}{y^4}

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