To approximate a solution of y′=y−x2 with y(0)=0.5, a student begins with an intended increment of 0.40. The increment is halved for any step in which ∣y′∣>1; otherwise the full increment is used. Using this rule until x=0.80 is reached, which of the following is the student’s final approximate value for y?
a) 0.820
b) 1.140
c) 0.916
d) 0.634