Which of the following is a quadratic function?
a. y = 4 ( x + 3 )
b. y = ( x - 5 ) ^2
c. y = 3x
d. y = -2 / x^2 + 1

A quadratic function is any function that can be written in the form:
y = ax^2 + bx + c ; where a, b, and c are real numbers and a = 0
A/ expression doesn't have x^2, so it's wrong
B/ y = (x-5)^2 = x^2 - 2.5.x + 5^2 = x^2 - 10x + 25
<=> y = x^2 - 10x + 25
So B is quadratic function
As for C and D they're not quadratic functions