Find the interval on which the curve y = x - ∫(1 to t) 5t² dt is concave upward. (Enter your answer using interval notation.)
(a) (-[infinity], -1) ∪ (1, [infinity])
(b) (-[infinity], -3) ∪ (-1, 1) ∪ (3, [infinity])
(c) (-[infinity], -2) ∪ (-1, 0) ∪ (1, 2) ∪ (3, [infinity])
(d) (-[infinity], -2) ∪ (-1, 0) ∪ (2, [infinity])
