Quadratic equation

If x1,x2 are the roots of x2-3x+a=0, and x3,x4 are those of the equationx2-12x++b=0, and x1,x2,x3 and x4 are in increasing G.P.,find a and b.

5 Answers

36
rahul ·

I think the question is incomplete.
We must be provided with the common ratio or something like that.....!!

71
Vivek @ Born this Way ·

OK. Proceed like this.

Say, x1 = ∂ , x2 = ∂r , x3 = ∂r2 and x4 = ∂r3

Then from the two equations, we have

∂ (1+r)= 3 and ∂r2 (1+r) = 12

Solving these two by Substitution, we have

r2 = 4

=> r = 2 ....... ( Since this is an increasing GP)

Substitute back in any of the results and get ∂ = 1

Hence the roots are :1,2,4,8.

Therefore, ∂2r = a

=> a = 2

and ∂2r5 = b

=> b = 32

36
rahul ·

@vivek - Must say, wonderful soln.
I didn't look at the question that way...!!

1
Vinay Arya ·

Thank you for this great solution.

71
Vivek @ Born this Way ·

Pehle main tumhe surrender karte dekh daar gaya tha.. Phir solve kiya toh ban gaya!!

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