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If mx2 + nx + c = 0 and px2 + qx + r = 0 have one root in common. If the sum and product of the roots which are different are 0 and 1 respectively, then what is the value of  ?
  • a)
    2np
  • b)
    4mp
  • c)
    2rc
  • d)
    4nq
Correct answer is option 'B'. Can you explain this answer?
Verified Answer
If mx2 + nx + c = 0 and px2 + qx + r = 0 have one root in common. If t...
Let α, β  be the roots of mx2 + nx + c = 0 and y, 6 be the roots of px2 + qx + r = 0


As these two quadratic equations have one root in common, let us assume that α = γ 




Adding (i) and (iii), we get,

But, β + δ = 0

Multiplying (ii) and (iv), we get,

But,  βδ = 1

Eliminating α from (v) and (vi), we get,

∴ 4crmp = [(-np) + (-mq)]2
∴ 4crmp = [n2p2 + m2q2 + 2npmq]
∴ 4 crmp - 4npmq = [n2p2+m2q2 - 2npmq]
∴  4mp(cr - nq) =  [np - mq]2

Hence, option 2.
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Most Upvoted Answer
If mx2 + nx + c = 0 and px2 + qx + r = 0 have one root in common. If t...
Let α, β  be the roots of mx2 + nx + c = 0 and y, 6 be the roots of px2 + qx + r = 0


As these two quadratic equations have one root in common, let us assume that α = γ 




Adding (i) and (iii), we get,

But, β + δ = 0

Multiplying (ii) and (iv), we get,

But,  βδ = 1

Eliminating α from (v) and (vi), we get,

∴ 4crmp = [(-np) + (-mq)]2
∴ 4crmp = [n2p2 + m2q2 + 2npmq]
∴ 4 crmp - 4npmq = [n2p2+m2q2 - 2npmq]
∴  4mp(cr - nq) =  [np - mq]2

Hence, option 2.
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