Which equation is quadratic in form?

6 (x + 2) 2 + 8x + 2 + 1 = 0

6x4 + 7x2 - 3 = 0

5x6 + x4 + 12 = 0

x9 + x3 - 10 = 0

Quadratic is

ax²+bx+c=0

first one the constants aren't added together

2nd one has power greater than 2

all of them have powers greater than 2

we can rewrite one of them to be quadratic

for the 2nd one

if we say that x²=u then we can rewrite it s

6u²+7u²-3=0

that is quadratic in form

I would say 2nd option