SOLUTION: Please I need help with: quintun was solving a quadestic equation in the form ax^2+bx+c=0 using the quadestic formula. He made the mistake, however, of switching a and c in the for

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Question 182933: Please I need help with: quintun was solving a quadestic equation in the form ax^2+bx+c=0 using the quadestic formula. He made the mistake, however, of switching a and c in the formula and and as a result he got answers that were 3 times the correct answer. Find the product of the roots of the quadratic equation
Answer by Edwin McCravy(20054) About Me  (Show Source):
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Please I need help with: quintun was solving a quadestic equation in the form ax^2+bx+c=0 using the quadestic formula. He made the mistake, however, of switching a and c in the formula and and as a result he got answers that were 3 times the correct answer. Find the product of the roots of the quadratic equation.
 

For any quadratic equation of the form

+matrix%281%2C7%2Cax%5E2%2C%22%2B%22%2Cbx%2C%22%2B%22%2Cc%2C%22=%22%2C0%29,

the product of the two roots is c%2Fa.

Suppose the two roots are p and q

Then matrix%281%2C3%2Cpq%2C+%22=%22%2C+c%2Fa%29

When he switched a and c in the
quadratic formula, he got the roots for

+matrix%281%2C7%2Ccx%5E2%2C%22%2B%22%2Cbx%2C%22%2B%22%2Ca%2C%22=%22%2C0%29,

to be 3p and 3q

So their product %283p%29%283q%29 is 9pq,

and that had to equal the number a%2Fc

so 9pq=a%2Fc

So we have the system:

system%28pq=c%2Fa%2C9pq=a%2Fc%29

Clearing of fractions:

system%28apq=c%2C9cpq=a%29

Solving each for the product pq

system%28pq=c%2Fa%2Cpq=a%2F%289c%29%29

So we have

c%2Fa=a%2F%289c%29

cross-multiplying gives:

9c%5E2=a%5E2

or

9c%5E2-a%5E2=0

so, factoring,

%283c-a%29%283c%2Ba%29=0

So either 3c=a or -3c=a

Now in the first case, substitution of

of 3c for a in 

matrix%281%2C3%2Cpq%2C+%22=%22%2C+c%2Fa%29

gives

matrix%281%2C3%2Cpq%2C+%22=%22%2C+c%2F%283c%29%29

matrix%281%2C3%2Cpq%2C+%22=%22%2C+1%2F3%29

---

In the second case, substitution of

of -3c for a in 

matrix%281%2C3%2Cpq%2C+%22=%22%2C+c%2Fa%29

gives

matrix%281%2C3%2Cpq%2C+%22=%22%2C+c%2F%28-3c%29%29

matrix%281%2C3%2Cpq%2C+%22=%22%2C+-1%2F3%29

So the product of the roots is either

1%2F3 or -1%2F3

Those are the answers!

----------------------------------------

If you want to demonstrate those answers in
specific cases, solve the quadratic equation:

6x%5E2-7x%2B2=0 and you'll find the solutions

and 2%2F3 and 1%2F2 which have 
product 1%2F3

Then switch a and c and you'll
get the equation

2x%5E2-7x%2B6=0 and you'll find that it has
solutions  2 and 3%2F2 which 
are 3 times the solutions 2%2F3 and 1%2F2.



Edwin