计算:(1+1/11+1/13+1/17)×(1/11+1/13+1/17+1/19)-(1+1/11+1/13+1/17+1/19)×(1/11+1/13+1/17).

问题描述:

计算:(1+

1
11
+
1
13
+
1
17
)×(
1
11
+
1
13
+
1
17
+
1
19
)-(1+
1
11
+
1
13
+
1
17
+
1
19
)×(
1
11
+
1
13
+
1
17
).

设x=

1
11
+
1
13
+
1
17

则原式=(1+x)×(x+
1
19
)-(1+x+
1
19
)x,
=x+
1
19
+x2+
1
19
x-x-x2-
1
19
x,
=
1
19