let a, b and c are unequal real positive numbers such that 2b = a + c, then roots of ax^2 + 2bx + c = 0 are

(i) real and equal (ii) Real and distinct (iii) imaginary (iv) nothing definite can be said

Plz explain

3 years ago


Answers : (3)


Dear student,


Sum of the roots=-2b/a


This shows the roots are real and distinct...

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Askiitians Expert

Sagar Singh

B.Tech, IIT Delhi


3 years ago

for any quadratic eq  ax2+bx+c roots are given by

 X = {-b+_ D)/2a

D =discriminant = (b2-4ac)1/2

our eq is ax2+2bx+c so

D = {(2b)2-4ac)1/2 ........1

2b = a+c  (given)

so , (2b)2 = (a+c)2 ...........2

putting  eq2 in eq1

D = { (a+c)2 - 4ac}1/2  =  { a2+c2-2ac}1/2 ={(a-c)2}1/2 =a-c

now roots are

 X = (-2b +_ D}/2a = {-2b + (a-c)}/2a     or        {-2b-(a-c)}/2a                                   

                           = -c/a                      or        -1                                  (on putting 2b =a+c )

so the roots are unequal & real

option (ii) is correct

3 years ago

the equation is ax^2+2bx+c=0

the discriminant is= B^2-4AC


discriminant= 4b^2-4ac

but 2b=a+c, therefore (2b)^2=(a+c)^2

= (a+c)^2-4ac



=(a-c)^2, which is always greater than zero

therefore roots are real and distinct

3 years ago

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