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Mathematics 7 Online
OpenStudy (kanwal32):

Sequence and Series question???????

OpenStudy (kanwal32):

If a,b,c are in AP and a^2,b^2,c^2 are in GP a<b<c and a+b+c=3/2 then value of a is

OpenStudy (kanwal32):

@ganeshie8 @ikram002p hlp

OpenStudy (kainui):

what is AP and GP?

OpenStudy (kainui):

Arithmetic and Geometric Progression?

OpenStudy (kanwal32):

Aritmetic Progression and Geometric Progession

OpenStudy (kanwal32):

yes

OpenStudy (kanwal32):

b=1/2

OpenStudy (kanwal32):

found out

OpenStudy (kanwal32):

a??????

OpenStudy (kainui):

Ok, well if a, b, and c are in an arithmetic progression, then that means there's some quantity you can add to a to get b and to b to get c. Similarly we can set up an equation for their squares in the GP.

OpenStudy (kanwal32):

YES

OpenStudy (kainui):

So make as many equations as you can and see if we can solve for anything.

OpenStudy (ikram002p):

well c-b=b-a \(c^2/b^2=b^2/a^2\)

OpenStudy (kanwal32):

yes

OpenStudy (ikram002p):

ok c+a-2b=0 2a+2b+2c=3 \(c^2 a^2=b^4\) \(ca=b^2\) ok u have 3 equations with 3 variables ^ solve

OpenStudy (kanwal32):

i have solved it this like but the answer is wrong

OpenStudy (kanwal32):

@ikram002p @Kainui @hartnn view this answer is \[\frac{ 1 }{2 }-\frac{ 1 }{ \sqrt{2} }\]

OpenStudy (kanwal32):

pls hlp

hartnn (hartnn):

ac = 1/4 a+c = 2b =1

hartnn (hartnn):

quadratic in a

OpenStudy (kanwal32):

yes i did this

OpenStudy (kanwal32):

c=2,a=-1

hartnn (hartnn):

getting a=b=c= 1/2 ...which are not acceptable values

OpenStudy (kanwal32):

no i got a=-1,b=1/2,c=2

hartnn (hartnn):

b^4 = (ac)^2 b^2 = +ac, b^2 =-ac ac = -1/4

OpenStudy (kanwal32):

yeah

hartnn (hartnn):

ac =-1/4 a+c =1/2 now you will get it

hartnn (hartnn):

a-1/(4a) = 1/2 solve

OpenStudy (aum):

I am getting the same too. a = b = c = 1/2. Satisfies all equations except they AP and GP unless a common difference of zero counts as AP and common ratio of 1 counts as GP.

OpenStudy (kanwal32):

ok so i didn't +- ok

hartnn (hartnn):

doesn't satisfy a<b<c aum

OpenStudy (aum):

Oh, yeah. Some mistake in this problem? or a typo?

OpenStudy (kanwal32):

yes @hartnn u r cprrect @aum 1/2 is not the answer

hartnn (hartnn):

no mistake a-1/(4a) = 1/2 did u get how i got this equation

OpenStudy (kanwal32):

yes @hartnn

hartnn (hartnn):

solve it, its a quadratic

hartnn (hartnn):

sorry, that should be a-1/(4a) = 1 because a+c = 2b =1

OpenStudy (anonymous):

@hartnn is righttt..btw hartnn cud u help me out

OpenStudy (kanwal32):

i got \[4a^2-4a+1\]

hartnn (hartnn):

a+c = 2b =1 ac = -b^2 , ac = b^2 ac =b^2 is rejected because a<b<c ac=-b^2 =-1/4

hartnn (hartnn):

you should get 4a^2 -4a-1 =0

OpenStudy (kanwal32):

wait let me check and figyre out ny nistake

OpenStudy (kanwal32):

ok

OpenStudy (kanwal32):

i didn't reject +b^2

OpenStudy (kanwal32):

got u hartnn

hartnn (hartnn):

4a^2 -4a-1 =0 will give you one root as your answer

OpenStudy (kanwal32):

got it

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