Elitmus
Exam
Numerical Ability
Number System
If (a^4)+(1/a^4)=119 then find value of (a^3)-(1/a^3)=????
Read Solution (Total 11)
-
- (a^4)+1/(a^4)=(a*a+1/a*a)(^2)-2=119
after solving we get as
(a-1/a)=3
so the value of (a^3)-(1/a^3)=(3)(1+11)=36
so ans is 36 - 10 years agoHelpfull: Yes(49) No(7)
- (a^4 + 1/a^4) = 119
(a^2 + 1/a^2)^2 = 119 + 2 = 121 => a^2 + 1/a^2 = 11
another eqn,
(a - 1/a) = sqrt(9) = 3
now,
a^3 - 1/a^3
= (a - 1/a)*(a^2 + a*1/a + 1/a^2)
= 3*(11+1)
= 36 - 10 years agoHelpfull: Yes(27) No(0)
- a^4+1/a^4=119
(a^2+1/a^2)^2-2.a.1/a=119
a^2+1/a^2=11
(a-1/a)^2+2.a.1/a=11
a-1/a=3
Now we Know a3 - b3 = (a - b)3 + 3 a b (a - b)
so,
(a^3)-(1/a^3)=(a-1/a)^3-3*a*1/a(a-1/a)=3^3-3*3=27-9=18
So the answer is 18 - 10 years agoHelpfull: Yes(26) No(22)
- a-1/a=3;
a^2+1/a^2=11;
so,
a^3-1/a^3=36 - 10 years agoHelpfull: Yes(1) No(0)
- Aaproxmatly 36
- 10 years agoHelpfull: Yes(1) No(1)
- 36 is the correct answer
- 10 years agoHelpfull: Yes(1) No(0)
- (a+b)^2= a^2+b^2+2ab
put b=1/a
(a+1/a)^2=a^2+1/a^2+2
(a+1/a)^2-2=a^2+1/a^2
use this formula u will get the answer=36
firstly +2 use u will get 121
& then -2 use u will get 9 - 10 years agoHelpfull: Yes(1) No(0)
- CANNOT BE DETERMINED??
- 10 years agoHelpfull: Yes(0) No(3)
- Ans- 36 is correct..This question came in Bank exam SBI PO-2013.
- 10 years agoHelpfull: Yes(0) No(0)
- (a^4)+1/(a^4)=(a*a+1/a*a)(^2)-2=119
after solving we get as
(a-1/a)=3
so the value of (a^3)-(1/a^3)=(3)(1+11)=36
so ans is 36
Read more at http://www.m4maths.com/placement-puzzles.php?ISSOLVED=&page=2&LPP=10&SOURCE=Elitmus&MYPUZZLE=&TOPIC=Numerical%20Ability&SUB_TOPIC=Number%20System#jY5PTuA3E8PZQx3c.99 - 10 years agoHelpfull: Yes(0) No(0)
- (x^2+1/x^2)^2 = x^4 + 1/x^4 + 2*x^2*1/x^2
= 119 +2
= 121
x^2+1/x^2 = 11
(x 1/x)^2 = x^2 + 1/x^2 2*x*1/x
= 11 2
= 9
x 1/x = 3
now (x1/x)^3 = x^3 1/x^3 3*x*1/x(x 1/x)
so x^3 1/x^3 = 3^3 + 3*3
= 27 +9
= 36
final ans is 36
- 9 years agoHelpfull: Yes(0) No(0)
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