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Answers:

A) d = 2

B) x = 1/2

Why?

We have dx2 + 5x - 3 = 0, and one solution is x = -3.

The equation is quadratic, so it can be factored into two linear terms (things that look like ax+b). Since,

x = -3

x + 3 = -3 +3

x + 3 = 0

So x + 3 is one of the terms.

So dx2 + 5x - 3 = 0 is equivalent to

(?x + ?)(x + 3) = 0

The first ? must be d since ?x*x = dx2. The second ? must be -1 since ?*3 = -3.

So we have

(dx - 1)(x + 3) = 0

When we distribute (students often know as F.O.I.L.), we find that

dx2+ 3dx - x - 3 = 0

dx2+ (3d-1)x - 3 = 0 (factor out x, or think of combining like terms) This is the same as:

dx2 + 5x - 3 = 0 So we know 3d - 1 = 5, an equation we can solve for d.

3d - 1 = 5

3d - 1 + 1 = 5 + 1

3d = 6

3d/3 = 6/3

d = 2

Yay! Part A of your problem is complete: d = 2.

Next, Part B, we must find the other root, or solution.

So now we have

2x2 + 5x - 3 = 0 is the same as

(2x - 1)(x + 3) = 0 so we know

2x - 1 = 0

2x - 1 + 1 = 0 + 1

2x = 1

2x/2 = 1/2

x = 1/2

So for Part B, we have x = 1/2 is the other root.

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