The correct options are
A f′(x)=0
B y=f(x) is a straight line parallel to x-axis
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∣∣33x3x2+2a23x3x2+2a23x3+6a2x3x2+2a23x3+6a2x3x4+12a2x2+2a4∣∣
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Applying, R2=R2−xR1,
=∣∣
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∣∣33x3x2+2a202a24a2x3x2+2a23x3+6a2x3x4+12a2x2+2a4∣∣
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Applying, C3=C3−2xC2,
=∣∣
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∣∣33x2a2−3x202a203x2+2a23x3+6a2x2a4−3x4∣∣
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Expanding by R2,
=2a2(6a4−9x4−4a4+9x4)=2a2(2a4)=4a6
So, f′(x)=0
y=f(x)=4a6=constant, so, it will be parallel to x-axis