Let an integer be 'x'
Then, its consecutive integer is (x + 1).
According to the question,
x(x + 1) = 90
x2 + x = 90
x2 + x - 90 = 0
x2 + 10x - 9x - 90 = 0
x(x + 10) -9(x + 10) = 0
(x + 10)(x - 9) = 0
x + 10 = 0 i.e. x = -10 and (x +1) = (-10 +1) = -9
or, x - 9 = 0 i.e. x = 9 and (x + 1) = (9 + 1) = 10
So, the required integers are -9 and -10 or 10 and 9.