We know that, a statement is a sentence which is either true or false but not both simultaneously.
(i) It is a false sentence, hence, it is a statement. (∵15+8=23)
(ii) y+9=7
It is not considered as a statement, since the value of y is not given.
(iii) It is false sentence, hence, it is a statement. (∵sin2x+cos2x=1)
(iv) It is a false sentence, hence, it is a statement.