The correct option is C (5x2+2x)−(7+5x2)=x2+2
The standard form of any quadratic equation is ax2+bx+c=0,
where a, b, c [coefficients] are real numbers and a≠0 [a is called the leading coefficient].
Option A: (x2+1)2=x4
⇒x4+2x2+1=x4
⇒2x2+1=0; This is a quadratic equation.
Option B: (x+1)2=x2
⇒x2+2x+1=x2
⇒2x+1=0; This is a linear equation.
Option C: (5x2+2x)−(7+5x2)=x2+2
⇒2x−7=x2+2
⇒x2−2x+9=0; This is a quadratic equation.
Option D: (x+2)3=4−x3
⇒x3+6x2+12x+8=4−x3
⇒2x3+6x2+12x+4=0
It's not a quadratic equation, it's a cubic equation as the highest power of x is of degree ‘3’.