If $f(x) = \cos([\pi^2]x) + \cos([- \pi^2]x)$,then which of the following is true?

If $A = \{x, y\}$,then the power set of $A$ is

Which of the following is the empty set?

In a survey of a town,it was found that $65 \%$ of the people surveyed watch the news on $T.V.$,$40 \%$ read a newspaper,and $25 \%$ read a newspaper and watch the news on $T.V.$ What percent of the people surveyed neither watch the news on $T.V.$ nor read a newspaper?

In a certain town,$25\%$ of families own a phone,$15\%$ own a car,and $65\%$ of families own neither a phone nor a car. If $2000$ families own both a car and a phone,consider the following statements:
$1$. $10\%$ of families own both a car and a phone.
$2$. $35\%$ of families own either a car or a phone.
$3$. $40,000$ families live in the town.
Which of the above statements are correct?

If $A$ and $B$ are any two non-empty sets and $A$ is a proper subset of $B$. If $n(A) = 4$,then the minimum possible value of $n(A \Delta B)$ is (where $\Delta$ denotes the symmetric difference of set $A$ and set $B$).