Đáp án C
y ' = 1. x 2 + 1 + x . 2 x 2 x 2 + 1 = x 2 + 1 + x 2 x 2 + 1 = ( x 2 + 1 ) + x 2 x 2 + 1 = 2 x 2 + 1 x 2 + 1
y " = 4 x . x + 2 1 − ( 2 x 2 + 1 ) . x x 2 + 1 x 2 + 1 = 4 x ( x 2 + 1 ) − ( 2 x 2 + 1 ) . x ( x 2 + 1 ) . x 2 + 1 = 2 x 3 + 3 x ( x 2 + 1 ) . x 2 + 1