check this

Active member

If l(m-n)x^2 + m(n-l)x + n(l-m) = o has equal roots, show that m = 2 l n /(l + n ).

Active member

clearly 1 is a root of the quadratic if the other root is also one then the product of the roots is also 1 so we have that
l,m,n form HP

or
m = 2 l n /(l + n ).
hence proved ..... Very Happy

Active member

cool answer, thnx.

Active member

can u explain how one root is 1.

Active member

its clear becoz 1 is satisfying the eq.

you need practice + concentrating to notice such things in ques. they help a lot in objective exams.....

you must be in class xi right..

Active member

no, i'll be going to std viii. am looking around to prepare best for NTSE. ANY SUGGESTIONS/HELP TO CRACK IT.

Active member

try buying some good books from universal or other good book store for ntse ...

best of luck . Very Happy

Active member

which book by universal? can u name please.i m in a city where nt many interested in NTSE

Active member

you may find books for ntse and their cost @

http://www.flipkart.com/search-books/ntse

Active member

are you in isc Xii or cbse XII?

Active member

hey quest..i cleared ntse myself 2 years ago so i can help u with it...the 2 books you MUST(u really must) have are
1)NTSE for class 8 by upkar
2)Tata Mcgraw Hill
if u can afford another then BMA Olympiad book will be gr8.

Active member

here are some tips which will surely help you...
1)Concentrate really hard on Mental Ability(it is the most scoring part)
2)Try to arrange for some CBSE class viii science buks(if u r not in cbse)and master the objective type ques.
3)History Geog ques are the easiest and the science part is the toughest...so prepare accordingly..

all the best afro

Active member

thank you so much johny

Active member

which class are you in?

Active member

hey jhony, i got tata mcgrawhill, but upkar and BMA nt available in my city.
thnks once again for book reccomendation.