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I think this the explanation isn't clear enough, please elaborate. Can some one please explain how is statement 1 manipulated into the 3 cases. I am not able to follow how the three cases have been formed and why they have been formed?

Thanks in advance!
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souvik101990
Official Solution:


Question prompt :

When a≠0, how many solutions does the equation \(a(x+b)^2+c=0\) have?

1) bc=0

2) |b|+|c|=0

--> Solving \(a(x+b)^2+c=0\) gives

\((x+b)^2 = (-c/a)\)

Now lets discuss each of the 3 cases one by one :


There are three cases to consider:

Case 1: \(a > 0\), \(c > 0\) or \(a < 0\), \(c < 0\)

The equation has no roots.

\((x+b)^2 = (-c/a)\) ---> LHS is positive number.

So we need RHS also positive.

\(a > 0\), \(c > 0\) ---> (-c/a) negative number.

\(a < 0\), \(c < 0\) ---> (-c/a) negative number.

So LHS can not be equal to RHS. No roots.



Case 2: \(c = 0\).

The equation has only one root.

\((x+b)^2 = (-c/a)\)

c= 0 then \((x+b)^2 = 0\)

This gives one root x = -b.



Case 3: \(a > 0\), \(c < 0\) or \(a < 0\), \(c > 0\)

The equation has two roots.

\((x+b)^2 = (-c/a)\) ---> LHS is positive number.

So we need RHS also positive.

\(a > 0\), \(c < 0\) ---> (-c/a) positive number. or

\(a < 0\), \(c > 0\) ---> (-c/a) positive number.

\((x+b)^2 = (-c/a) = K\)

So roots will be \(x = -b +/- \sqrt{k}\)



Condition 1):

If \(bc = 0\), then when

\(a = 1\), \(b = 0\), \(c = -1\), the equation has two roots, and when

\(a = 1\), \(b = 0\), \(c = 0\), the equation has one root.

As the question does not have a unique answer, condition 1) is not sufficient.



Condition 2)

\(|b| + |c| = 0\) ⇔ \(b = c = 0\).

Since \(c = 0\), the equation has only one root.

Condition 2) is sufficient.



Therefore, the answer is B.

Answer: B

ridhi9jain

I have tried to breakdown the OE 3 cases...

Hope that helps!!
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ridhi9jain
I think this the explanation isn't clear enough, please elaborate. Can some one please explain how is statement 1 manipulated into the 3 cases. I am not able to follow how the three cases have been formed and why they have been formed?

Thanks in advance!


souvik101990
Official Solution:


Question prompt :

When a≠0, how many solutions does the equation \(a(x+b)^2+c=0\) have?

1) bc=0

2) |b|+|c|=0

--> Solving \(a(x+b)^2+c=0\) gives

\((x+b)^2 = (-c/a)\)

Now lets discuss each of the 3 cases one by one :


There are three cases to consider:

Case 1: \(a > 0\), \(c > 0\) or \(a < 0\), \(c < 0\)

The equation has no roots.

\((x+b)^2 = (-c/a)\) ---> LHS is positive number.

So we need RHS also positive.

\(a > 0\), \(c > 0\) ---> (-c/a) negative number.

\(a < 0\), \(c < 0\) ---> (-c/a) negative number.

So LHS can not be equal to RHS. No roots.



Case 2: \(c = 0\).

The equation has only one root.

\((x+b)^2 = (-c/a)\)

c= 0 then \((x+b)^2 = 0\)

This gives one root x = -b.



Case 3: \(a > 0\), \(c < 0\) or \(a < 0\), \(c > 0\)

The equation has two roots.

\((x+b)^2 = (-c/a)\) ---> LHS is positive number.

So we need RHS also positive.

\(a > 0\), \(c < 0\) ---> (-c/a) positive number. or

\(a < 0\), \(c > 0\) ---> (-c/a) positive number.

\((x+b)^2 = (-c/a) = K\)

So roots will be \(x = -b +/- \sqrt{k}\)



Condition 1):

If \(bc = 0\), then when

\(a = 1\), \(b = 0\), \(c = -1\), the equation has two roots, and when

\(a = 1\), \(b = 0\), \(c = 0\), the equation has one root.

As the question does not have a unique answer, condition 1) is not sufficient.



Condition 2)

\(|b| + |c| = 0\) ⇔ \(b = c = 0\).

Since \(c = 0\), the equation has only one root.

Condition 2) is sufficient.



Therefore, the answer is B.

Answer: B

ridhi9jain

I have tried to breakdown the OE 3 cases...

Hope that helps!!
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Paugustin90
Not sure if I get the break down of the question. Can you please explain how you broke it down in a different way?

Paugustin90

Question prompt :

When a≠0, how many solutions does the equation \(a(x+b)^2+c=0\) have?

1) bc=0

2) |b|+|c|=0

St 1 : bc = 0 so b= 0 or c= 0 or both b and c = 0.

c=0 gives \(a(x+b)^2+0=0\) ----> x = -b

Both b= 0 and c= 0 gives \(a(x+0)^2+0=0\) -----> x =0

2 different answers. We can eliminate st 1. Option A and D are gone.

For sack of completeness of discussion when b =0, it gives\(x^2 = (-c/a)\) - So 2 roots or no roots. (As discussed in my earlier post above).

St 2: |b|+|c|=0

This gives b = 0 and c = 0

So \(a(x+0)^2+0=0\) -----> x =0

Only one possible values for x.

Sufficient.

Ans : B

Hope this helps!!
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the equation is
ax^2 + 2abx +(ab^2+c)
the roots are
[(-b +- sqrt(b^2-4ac)]/2a

solving this we get the two roots as
c-1
-(c+1)

so if c =0 then we can get one root.
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