Which equation is quadratic in form?

2 (x + 5) 2 + 8x + 5 + 6 = 0

x6 + 6x4 + 8 = 0

7x6 + 36x3 + 5 = 0

4x9 + 20x3 + 25 = 0

A quadratic form is a polynomial having a degree of two in n variables. They are called unary, binary and ternary forms. Quadratic forms has an important place in a wide range of application in mathematics. The equation that has a quadratic equation is:

2 (x + 5) ^2 + 8x + 5 + 6 = 0