The integral of sin(x) is -cos(x). To evaluate the definite integral from 0 to π/2, we compute [-cos(x)] evaluated from 0 to π/2. This equals [-cos(π/2)] - [-cos(0)]. Since cos(π/2) = 0 and cos(0) = 1, the expression becomes [0] - [-1] = 1. Option 1 is incorrect as it represents the integral of sin(x) over a full period or certain symmetric intervals. Option 2 is a sign error. Option 4 incorrectly treats the function as a constant.