Ta có:
+ \(x = 5, y = –7\) thì \(x . y = 5. ( –7) = – (5 . 7) = –35.\)
+ \(x = –18, y = 10\) thì \(x . y = (–18) . 10\)\( = – (18 . 10) = –180.\)
+ \(y = –10 ;\)\(x.y = x . (–10) = – (x.10) = – 180,\) do đó \(x . 10 = 180\) nên \(x = 18.\)
+\( x = –25; x.y = (–25).y = –(25.y) = –1000,\) do đó \(25.y = 1000\) nên \(y = 40.\)
Ta có bảng sau:
|
x
|
5
|
-18
|
18
|
-25
|
|
y
|
-7
|
10
|
-10
|
40
|
|
x . y
|
-35
|
-180
|
-180
|
-1000
|
