Which of the following equations is quadratic?

x (x2 + 1) = 0

(x + 3) (x + 4) = 5

5 (4 x + 2) = 3

the first one

x (x2 + 1) = 0

I think it's 2 because the quadratic equation looks like this ax^2+bx+c=0 and option 2 looks like it.

Step-by-step explanation:

For option 1: x (x^2+1) = 0

x^3+1=0 (This also does not look like the quadratic function, so it couldn't be the answer)

For option 2: (x+3) (x+4) = 5

x^2+3x+3x+12=5

x^2+6x+12=5 (This does look like the quadratic function, so it could be the answer)

For option 3:

5 (4x+2) = 3

20x+10=3 (This also does not look like the quadratic function, so it couldn't be the answer)