Question

Which equation is a quadratic equation?

y + 3 = 5x + 10

y + 4x2 = (4x − 2)(x + 3)

y − 8x = (x2 + 1)(9x − 7)

y = 2x + 7x(x + 1)

Answer 1

@satellite73

Answer 2

@phi

Answer 3

what makes an equation "quadratic" ?

Answer 4

The squared variable?

Answer 5

its highest degree (exponent) is 2. It has a 2nd degree term

squared variable YES

Answer 6

so if there is only x^1 or no x, cross it off the list.

Answer 7

That leaves the middle two.

Answer 8

if you multiply x times x^2 or higher you will get x^3 or higher. that is too high. cross those off the list

Answer 9

I would not cross off the bottom

multiplying x*x gives x^2 so that is ok

Answer 10

The third one?

Answer 11

the 3rd one has (x^2 + 1)(9x − 7)
notice you will end up multiplying x^2 times 9x to get 9x^3
no. the exponent is 3 (too big)

Answer 12

it will be 2nd or 4th

the 4th is definitely quadratic... you can multiply it out and simplify and it looks like a very respectable quadratic (you could take it home to meet the folks)

Answer 13

LOL, love the last line. Thanks!

Answer 14

the 2nd one is tricky.

can you multiply it out and simplify it ?

y + 4x^2 = (4x − 2)(x + 3)

Answer 15

I forgot how to do that.

Answer 16

on the right side of the =, use FOIL
(4x -2)(x+3)
First: 4x * x = 4x^2
Outer: 4x * 3= 12x
Inner: -2 * x = -2x
Last: -2*3 = -6
add up:
4x^2 + 10 x -6

so you now have
y + 4x^2 = 4x^2 + 10 x -6

can you simplify to y = ....
?

Answer 17

you would add -4x^2 to both sides
\[ y + 4x^2 -4x^2 = 4x^2 -4x^2 + 10 x -6 \]
can you simplify ?