Problema Solution

find the quadratic equation whose roots are -3 and 1/5 and whose value at x =0 is -3.

Answer provided by our tutors

let the quadratic equation be


ax^2 + bx + c = 0, where a,b,c are constants


we know that for x=0 the value is -3 that is


a*0^2 + b*0 + c = -3


c = -3


Now we need to find a and b.


Since -3 and 1/5 are the roots if we replace for x = -3 or x = 1/5 the value must be 0 that is


for x = -3


a(-3)^2 - 3b - 3 = 0


9a - 3b - 3 = 0


for x = 1/5


a(1/5)^2 + b(1/5) - 3 = 0


a/25 + b/5 - 3 = 0


by solving the system of equations


9a - 3b - 3 = 0

a/25 + b/5 - 3 = 0


we find


a = 5


b = 14


therefore the quadratic equation is


5x^2 + 14x - 3 = 0