Hey Deci.
Hint: Remember that you can use 0 for the x term coefficients as well as the final coefficient (c value). I don't think you factored this in.
So, the question is :
If 3 different numbers are taken from the set {0,1,3,5,7} to be used as the coefficient of a standard quadratic equation
a) How many such quadratic equations can be formed?
b) How many of these have real roots
I have work on it, but the result is different from the answer key.. So anyone please help me what I've done wrong...
This is what i've done
and I got 60+12+12 = 84 equations for (a) and 18 equations for (b)
but the book says it should be 88 for (a) and 28 for (b)
There are 4 choices for digits for (since ). That leaves 4 digits for . Once you choose that, there are 3 digits left for . So, there are 4*4*3=48 quadratic equations, which is much fewer than the 88 the book counted. Are you sure the digits should be different?