Quantitative aptitude

07 September 2011

1).if sum of first n terms of an a.p is 2n^2+n then difference of its tenth & first term is :

ans:36.

2).g is a g.m between a & b then 1/g^2-a^2+1/g^2-B^2=

ans:1/g^2.

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4 Replies

intermediate(ipc)course (no) (1460 Points)
Replied 07 September 2011

pl solve those problems.

Mukesh Kumar Singh (CA-FINAL) (4094 Points)
Replied 07 September 2011

sign used in your problem is not proper, so you can post scanned copy of your querry.

intermediate(ipc)course (no) (1460 Points)
Replied 07 September 2011

there is no wrong in sign of problems.please solve this.g^2 means g square.

Ankit Hinduja (Student) (1227 Points)
Replied 08 September 2011

for 2.

1/(g^2-a^2) + 1/(g^2-b^2)

=1/(g^2-g^4/b^2) + 1/(g^2-b^2) ( gis G.M., so,g^2=ab, g^4=a^2b^2,so a^2=g^4/b^2..in this step we have substituted a^2)

=b^2/(g^2 b^2-g^4) + 1/(g^2-b^2)(by solving the denominator,b^2 goes to the numerator)

=b^2/-g^2(g^2-b^2) + 1/(g^2-b^2)( -b square is taken out commen in denominator).

=(b^2-g^2)/-g^2(g^2-b^2) ((taking (g^2-b^2) as LCM and solving the fraction ))

=1/g^2 (( in the numerator we take out (-) sign common so, (g^2-b^2)gets cancelled ))

=1/g^2

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