A glance could give the solution

Algebra Level 2

If a x = b y = c z a^x = b^y = c^z for distinct values of a , b , c a,b,c with a b c = 1 abc=1 , then find the value of x y + y z + x z xy + yz +xz .


The answer is 0.

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2 solutions

Shivamani Patil
May 15, 2015

Let a x = b y = c z = k { a }^{ x }={ b }^{ y }={ c }^{ z }=k\quad

a = k 1 x , b = k 1 y , c = k 1 z \Rightarrow a={ k }^{ \frac { 1 }{ x } },b={ k }^{ \frac { 1 }{ y } },c={ k }^{ \frac { 1 }{ z } }

a b c = k 1 x + 1 y + 1 z = k x z + x y + z y x y z = 1 \Rightarrow abc={ k }^{ \frac { 1 }{ x } +\frac { 1 }{ y } +\frac { 1 }{ z } }={ k }^{ \frac { xz+xy+zy }{ xyz } }=1

x z + x y + z y x y z = 0 \Rightarrow \frac { xz+xy+zy }{ xyz } =0

x z + x y + z y = 0 \therefore xz+xy+zy=0

It must be mentioned that x , y , z 0 x,y,z \neq 0 .

Nihar Mahajan - 6 years, 1 month ago

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Ya also that a,b,c are distinct.

shivamani patil - 6 years, 1 month ago

sorry for the inconvenience , @Nihar Mahajan i just forgot to mention that because i was busy in some work so i just put up the question quickly ...

Palash Som - 6 years ago

I'm sorry, but if a = b = c = 1 a=b=c=1 and also x = y = z = 1 x=y=z=1 , I dont see how 1 + 1 + 1 = 0 1+1+1=0

Or generally if a = b = c = 1 a=b=c=1 then any value of x,y, and z satisfies this equation.

Vishnu Bhagyanath - 6 years, 1 month ago

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So I think that the problem poser must mention that a , b , c a,b,c are distinct .

Nihar Mahajan - 6 years, 1 month ago

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Certainly.

Vishnu Bhagyanath - 6 years, 1 month ago

I also made the same mistake and this question is totally flawed.

Arian Tashakkor - 6 years, 1 month ago

Nice solution!

Sravanth C. - 6 years, 1 month ago

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Thank you friend.

shivamani patil - 6 years ago

Good solution !!

Swapnil Das - 6 years ago

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Thank you.

shivamani patil - 6 years ago

You assumed a x + b y + c z = k { a }^{ x }+{ b }^{ y }+{ c }^{ z }=k and then implied that a = k 1 x , b = k 1 y , c = k 1 z a=k^{\frac{1}{x}}, b=k^{\frac{1}{y}}, c=k^{\frac{1}{z}} . But if yo substitute the later into the former you get 3 k = k 3k=k .

Miguel Sanchez - 6 years ago

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Sry it was a typo I have fixed it.

shivamani patil - 6 years ago

can we put K=1 if yes than (xy + yz+xz)/xyz= 1

Gaurav Purswani - 6 years ago
Felix Belair
Jan 26, 2020

I just said: imagine if a is 1, and b and c are inverses of each other, so the product of all 3 give 1. Then if x y and z is 0. Well they all give 1. so xy+yz+xz is 0

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