Flag 9 grade maths> If xcube + 1/xcube = 110, then x+1/x = ?...
question mark

If xcube + 1/xcube = 110, then x+1/x = ?

Sidharth Mathur , 9 Years ago
Grade 9
anser 5 Answers
Hasan Naqvi

Last Activity: 9 Years ago

let x + 1/x =n
 
then 
(x + 1/x) 3 =n3
= x3 + 1/x3 + 3 * x * 1/x2 + 3 * x2 * 1/x
=110 + 3/x + 3x
=110 + 3(x + 1/x )
=110 + 3n
 
Now solving,
n3= 110 +3n
n3 – 3n -110 = 0
Putting n =5(one of the factors of 110), we this eqn to reduce to 0
So dividing this equation by n-5
(n-5)(n- 5n + 22) = 0
Since the quadratic equation has no real answer, 
 
I guess x + 1/x = 5
 

abhinav

Last Activity: 8 Years ago

Let x+1/x be y - [1]Then (x+1/x)³=x³+1/x³+3(x+1/x)y³=110+3y [from 1and x³+1/x³=110]y³ here is a perfect cube as we know y. Therefore we must find a number whose whose cube is near 110 and greater than 110 by 3 times of it. So the cube of 5 is is very near to 110 which is 125 and on subtracting 110 we get 15 which can be written as 3 x 5. So y equal to 5. So 5 is the required answer.

boom

Last Activity: 7 Years ago

lollololololololol
lollololololololol
lollololololololol
lollololololololol
lollololololololol
lollololololololol
lollololololololol
lollololololololol

boom

Last Activity: 7 Years ago

lollololololololollollololololololollollololololololollollololololololollollololololololollollololololololollollololololololollollololololololollollololololololollollololololololollollololololololollollololololololollollololololololollollololololololollollololololololol
 

boom

Last Activity: 7 Years ago

I RULE 
I RULE 
I RULE 
I RULE 
I RULE 
I RULE 
I RULE 
I RULE 
I RULE 
I RULE 
I RULE 
I RULE 
I RULE 
I RULE 
I RULE 
I RULE 
I RULE 
I RULE 
I RULE 
I RULE 
I RULE 
I RULE 
I RULE 
I RULE 
I RULE 
I RULE 
 
 

Provide a better Answer & Earn Cool Goodies

star
LIVE ONLINE CLASSES

Prepraring for the competition made easy just by live online class.

tv

Full Live Access

material

Study Material

removal

Live Doubts Solving

assignment

Daily Class Assignments


Ask a Doubt

Get your questions answered by the expert for free