The correct options are
B 2x2=−1
C −x2+x+4x2=−3
A quadratic equation in variable x is of the form ax2+bx+c=0, where a, b, c are real numbers and a ≠ 0.
Equation −x+x3+4x2=0 has third power of x and in equation −x+12=0, a=0. So, these equations are not in the above mentionaed form and hence are not quadratic.
Equation 2x2=−1 can be written as 2x2+0x+1=0. It is of the above mentioned form and hence is quadratic.
Also, equation −x2+x+4x2=−3 can be simplified and written as 3x2+x+3=0 and hence is quadratic.