Elitmus
Exam
Numerical Ability
Log and Antilog
how many solution for x....
1/2(log6(x^2-8x+16)+1/2(log6(x^2-9x+81)=1
a)0
b)1
c)3
d)4
Read Solution (Total 10)
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- >>log6((x-4)(x-9))=1.....(i)
>>log6((x-4)(x-9))=log6(6)
>>(x-4)(x-9)=6
by solving..x=3,10
eqn (i) is true for x=10, not for x=3
because, log(ab)=log(a)+log(b)
so, only 1 solution for x=10.
ans-b - 10 years agoHelpfull: Yes(23) No(4)
- and
in place of 9x ,it was 18x - 10 years agoHelpfull: Yes(12) No(1)
- 1/2(log6(x^2-8x+16)+1/2(log6(x^2-9x+81)=1
1/2(log6(x^2-8x+16)+(log6(x^2-9x+81)))=1 , takng 1/2 common
log6(x^2-8x+16)+log6(x^2-9x+81)=2
log6((x^2-8x+16)(x^2-9x+81))=2 , acc to log rule log a + log b = log(a+b)
log6((x-4)^2(x-9)^2)=2
log6((x-4)(x-9))^2=2
2log6((x-4)(x-9))=2
log6((x-4)(x-9)) = 1
(x-4)(x-9)=6
x^2-13x+36 = 6
x = 3,10
so, there are two solns....
- 10 years agoHelpfull: Yes(10) No(19)
- in place of 9x ,it was 18x.
by solving both the eq,we will get
log6((x-4)(x-9))=1
value of x will be 3
it will have only 1 solution - 10 years agoHelpfull: Yes(8) No(3)
- 1/2(Log6(x^2-8x+16))+1/2(Log6(X^2-9x+81))=1
1/2(Log6(x-4)^2)+1/2(Log6(x-9)^2)=1
log6((x-4)^2*(x-9)^2))=2log6(6)
so,
((x-4)^2)((x-9)^2)=6^2
either (x-4)^2=36 or (x-9)^2=36
if:(x-4)^2=36
x-4=+6 or x-4=-6
so, x=10 or x=-2
if:(x-9)^2=36
x-9=+6 or x-9=-6
so, x=15 or x= 3
number of solution is:4
- 10 years agoHelpfull: Yes(6) No(10)
- log rule was (log a + log b) = log(a*b)
- 10 years agoHelpfull: Yes(3) No(0)
- if u hv sm common sense thn don't wrt wrng qstns
- 10 years agoHelpfull: Yes(1) No(2)
- b,loga+logb=logab
- 10 years agoHelpfull: Yes(0) No(0)
- there is no solution for this q . so ans is a) zero
- 9 years agoHelpfull: Yes(0) No(1)
- Ans is b.
It satisfy for only 10 not for 3.
As, log6((x-4)(x-9))=log6(6)
Put x = 10 in above equation
log 6 base 6 = log 6 base 6
Hence proved. ;) - 7 years agoHelpfull: Yes(0) No(1)
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