Lost Logarithm III

Algebra Level 1

x y = 1 0 a , y z = 1 0 b , x z = 1 0 c \large \color{#20A900}x \color{#624F41}y=10^a, \quad \color{#624F41}y \color{#D61F06}z=10^b, \quad \color{#20A900}x \color{#D61F06}z=10^c

Consider the system of equations above, what is log x + log y + log z \log \ \color{#20A900} x +\log \ \color{#624F41}y+ \log \ \color{#D61F06}z ?

Details and Assumptions :

The logarithms have base of 10 10

a + b + c 2 \dfrac{a+b+c}{2} 2 ( a + b + c ) 2(a+b+c) a + b + c 4 \dfrac{a+b+c}{4} a + b + c a+b+c

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7 solutions

Danish Ahmed
Mar 18, 2015

Taking the product of the equations we get

x 2 y 2 z 2 = 1 0 a + b + c x^2y^2z^2=10^{a+b+c} .

Hence taking logs of both sides,

log ( x 2 y 2 z 2 ) = a + b + c \log (x^2y^2z^2)=a+b+c

or 2 log ( x y z ) = a + b + c 2\log (xyz)=a+b+c

or log x + log y + log z = a + b + c 2 \log x+\log y+\log z=\dfrac{a+b+c}{2}

Wow! Nice solution!

Joel Yip - 6 years, 2 months ago
Ahmad Sofiullah
Mar 19, 2015

Given, xy=10^a

log(xy)=log10^a (Taking log of each side)

log x + log y= a .............(1)

So we can say respectively,

log y + log z= b ..........(2)

log z + log x= c ...........(3)

(1)+(2)+(3) we get,

log x + logy + logy + log z + log z +log x =a+b+c

2(log x + logy + log z) = a+b+c

log x + logy + log z = (a+b+c)/2

Gamal Sultan
Mar 26, 2015

(xy)(yz)(xz) = 10^(a + b + c)

(xyz)^2 = 10^(a + b + c)

2log(xyz) = a + b + c

log(xyz) = (a + b + c)/2

log x + log y + log z = ( a + b + c)/2

Sir ,please tell me that log(xyz)=logx +log y + log z ?????

Aman Real - 6 years, 2 months ago

(x^2) (y^2) (z^2)=10^a+b+c

log(x^2) (y^2) (z^2)=a+b+c

2log(xyz)=a+b+c

log(xyz)=(a+b+c)/2

log x+log y+log z=(a+b+c)/2

Atika Samiha
Mar 26, 2015

log x+log y+log y+log z+log z+log x= a log10+b log10+c log10. or,2(log x+log y+log z)=a+b+c. or,log x+log y+log z=(a+b+c)/2

Awais Younus
Mar 19, 2015

logx+logy=a logy+logz=b logx+logz=c adding these 3 2logx+2logy+2logz=a+b+c 2(logx+logy+logz)=a+b+c logx+logy+logz=a+b+c/2

Raafat Mouhareb
Mar 19, 2015

log x+log y = a log 10 .........(1) log y+log z= b log 10 .........(2) log x+log z = c log 10 .........(3) summing (1).(2).(3) 2 log x+ 2 log y+ 2 log z= a + b + c dividing by 2 log x+ log y+ log z= (a + b + c)/2

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