Which of the following is non-negative number?  Choose the correct option
A) (a-0.9)(a-1)  B) (a+1)(a-1)  C) (a+0.9)(a+1)  D) (a-0.6)(a-0.6)  E) a(a+1)
5-sec approach:   D. (a-0.6)(a-0.6) = (a-0.6)^2. The square of a number is always non-negative.   Answer: (a-0.6)(a-0.6).
<result>D</result>
Which of the following is non-negative number?