If 2 7 x = 6 4 y = 1 2 5 z = 6 0 , find the value of x y + y z + x z 2 0 1 3 x y z .
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Note that we can take the x,y,z-th root because x,y,z are positive numbers. (not necessary greater than 1.)
Wonderful and elegant !!
yes, I too did it the same way
did the exact same way.... the best solution, indeed
2 7 x = 6 4 y = 1 2 5 z = 6 0 ∴ x = lo g 2 7 6 0 , y = lo g 6 4 6 0 , z = lo g 1 2 5 6 0 N o w , x y + y z + z x 2 0 1 3 x y z = x 1 + y 1 + z 1 2 0 1 3 ( D i v i d i n g n u m e r a t o r a n d d e n o m i n a t o r b y x y z ) ∴ x y + y z + z x 2 0 1 3 x y z = lo g 2 7 6 0 1 + lo g 6 4 6 0 1 + lo g 1 2 5 6 0 1 2 0 1 3 = lo g 6 0 2 7 + lo g 6 0 6 4 + lo g 6 0 1 2 5 2 0 1 3 = 3 lo g 6 0 ( 3 × 4 × 5 ) 2 0 1 3 = 3 lo g 6 0 ( 6 0 ) 2 0 1 3 = 3 2 0 1 3 = 6 7 1
Did the same!!!
I also did the same solution.
Did the same
Firstly, we have no direction on how to solve this problem, we can either handle
2 7 x = 6 4 y = 1 2 5 z = 6 0
or
x y + y z + x z 2 0 1 3 x y z
We cannot really see the connection between these two expressions and the first equation seems complicated if we touch it. So, what I did is simplify the second expression:
x y + y z + x z 2 0 1 3 x y z
= 2 0 1 3 ( x y z x y + y z + x z 1 )
= 2 0 1 3 ( x 1 + y 1 + z 1 1 )
Now, the expression become more simpler, the connection between them is as below
6 0 x 1 = 2 7
6 0 y 1 = 6 4
6 0 z 1 = 1 2 5
Then, we do as below:
6 0 x 1 + y 1 + z 1 = 3 3 × 4 3 × 5 3 = 6 0 3
So,
x 1 + y 1 + z 1 = 3
Substitute this to the given expression we have:
= 2 0 1 3 ( x 1 + y 1 + z 1 1 )
= 2 0 1 3 ( 3 1 )
= 6 7 1
2 7 x = 3 3 x = 6 4 y = 2 6 y = 1 2 5 z = 5 3 z = 6 0 and on multiplying 3 equations we get [ 3 x ∗ ( 2 2 ) y ∗ 5 z ] 3 = 6 0 3 and further we get 3 x ∗ 2 2 y ∗ 5 z = 3 1 ∗ 2 2 ∗ 5 1 and hence we get x = y = z = 1 and then ( x y + y z + x z ) 2 0 1 3 ∗ x ∗ y ∗ z = 3 2 0 1 3 = 6 7 1
If x = y = z = 1, then we have 27 = 64 = 125 = 60.
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Since we get 3 equations, we can say that 2 7 x = 6 0 , 6 4 y = 6 0 , 1 2 5 z = 6 0 .
Take a x,y,z-th root we get...
2 7 = 6 0 x 1 , 6 4 = 6 0 y 1 , 1 2 5 = 6 0 z 1 .
We multiply 3 equations we get...
2 7 × 6 4 × 1 2 5 = 6 0 x 1 + y 1 + z 1
6 0 3 = 6 0 x 1 + y 1 + z 1
x 1 + y 1 + z 1 = 3 ....
Simplify that we get x y z x y + y z + z x = 3
x y + y z + z x x y z = 3 1
Therefore: x y + y z + z x 2 0 1 3 x y z = 3 2 0 1 3 = 6 7 1 ~~~