Question

Question 20 of 25

1 Point
After being rearranged and simplified, which equation cannot be solved using
the quadratic formula?
O
O
A. x2 - 6x- 7 = 2x
B. 2x2 – 3x+ 10 = 2x2 + 21
O
C. 5x2 – 3x + 10 = 2x2
O D. 2x - 4 = 2x2

Answer 1

B.
`2x^(2)-3x+10=2x^(2)+21`

Explanation:

A quadratic equation is of the form
`ax^(2) +bx +c=0`, where, a,b and c are any real numbers and
`a\\e 0`.

The quadratic formula is given as:

`x=\frac{-b\pm \sqrt{b^(2)-4ac}}{2a}`

Here, the value of
`a` can't be 0.

Now, the necessary condition to check if quadratic formula can be used in the given equations is to check the value of
`a` after rearranging them in the standard form.

Let us check each expression for the value of
`a`.

Option A:

`x^(2)-6x-7=2x\\x^(2)-6x-2x-7=0\\x^(2)-8x-7=0`

Here,
`a=1`. So, we can use quadratic formula.

Option B:

`2x^(2)-3x+10=2x^(2)+21\\ 2x^(2)-2^(2)-3x+10-21=0\\0x^(2)-3x-11=0`

Here,
`a=0`. So, we can't use quadratic formula.

Option C:

`5x^(2)-3x+10=2x^(2)\\5x^(2)-2x^(2)-3x+10=0\\3x^(2)-3x+10=0`

Here,
`a=3`. So, we can use quadratic formula.

Option D:

`2x-4=2x^(2)\\-2x^(2)+2x-4=0`

Here,
`a=-2`. So, we can use quadratic formula.

So, only option B has
`a=0`. So, we can't use quadratic formula for option B.