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GRE - Quantitative Reasoning - Quadratic Equations

If one root of x^2+px+12=0 is 4, and the equation x^2+px+q=0 has equal roots then the value of q is

If one root of x^2 px 12=0 is 4, and the equation x^2 px q=0 has equal roots then the value of q is

A. 49/4
B. 4/49
C. 4
D. 1/4
E. 12

 

Given that -

4 is a root of  x2 + px + 12 = 0

substituting 4 in the equation to get the value of p

42 + 4p + 12 = 0

p = -7

Substituting value of p in the second equation

x2 - 7x + q = 0

given that the roots are equal

i.e. discriminant = 0

(-7)2 - 4*1*q = 0

q = 49/4

Option A is correct