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## Comment on

Quadratic Equations## @0:33 How did you get x^2

## All we're saying here is that

All we're saying here is that x^2 + 7x = 0 is a quadratic equation, since we can rewrite this equation in the form ax^2 + bx + c = 0

## In the question 9x^2 + 6x + 1

## That's a valid approach too.

That's a valid approach too.

## If 2ab - c = 2a(b - c), which

(A) a=0 and c=0

(B) a=1/2 and b=2

(C) b=1 and c=0

(D) a=1 or b=0

(E) a=1/2 or c=0 The answer is E but I fell it could be c also as I started putting figures with c equation and came equal so I choose c .

## Given: 2ab - c = 2a(b - c)

Given: 2ab - c = 2a(b - c)

Expand right side: 2ab - c = 2ab - 2ac

Subtract 2ab from both sides: -c = -2ac

Add 2ac to both sides: 2ac - c = 0

Factor: c(2a - 1) = 0

So, EITHER c = 0, OR 2a - 1 = 0

If 2a - 1 = 0, then a = 1/2

So, either c = 0 or a = 1/2 (answer choice E)

The keyword is MUST. Although b = 1 and c = 0 (answer choice C) is a valid solution, it need not be the case that b = 1. Notice that b = 0 and c = 0 also works.

## Thanx for the explaination .

## How did you get 169?

## You're referring to 6:05 in

You're referring to 6:05 in the video.

We have 3² - (4)(10)(-4) = 9 - (-160)

= 9 + 160

= 169

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