问题 解答题
计算.
(1)1+4
1
6
+7
1
12
+10
1
20
+13
1
30
+16
1
42
+19
1
56
+22
1
72
+25
1
90

(2)(
17
11
+
18
21
+
19
31
+
20
41
)×(
18
21
+
19
31
+
20
41
+
21
51
)-(
17
11
+
18
21
+
19
31
+
20
41
+
21
51
)×(
18
21
+
19
31
+
20
41
)
答案

(1)1+4

1
6
+7
1
12
+10
1
20
+13
1
30
+16
1
42
+19
1
56
+22
1
72
+25
1
90

=(1+4+7+10+13+16+19+22+25)+(

1
6
+
1
12
+
1
20
+
1
30
+
1
42
+
1
56
+
1
72
+
1
90
),

=117+(

1
2
-
1
3
+
1
3
-
1
4
+
1
4
-
1
5
+
1
5
-
1
6
+
1
6
-
1
7
+
1
7
-
1
8
+
1
8
-
1
9
+
1
9
-
1
10
),

=117+(

1
2
-
1
10
),

=117+

2
5

=117

2
5

(2)设

17
11
+
18
21
+
19
31
+
20
41
=a,
18
21
+
19
31
+
20
41
=b,则a-b=
17
11
+
18
21
+
19
31
+
20
41
-(
18
21
+
19
31
+
20
41
)=
17
11
,那么:

(

17
11
+
18
21
+
19
31
+
20
41
)×(
18
21
+
19
31
+
20
41
+
21
51
)-(
17
11
+
18
21
+
19
31
+
20
41
+
21
51
)×(
18
21
+
19
31
+
20
41
),

=a×(b+

21
51
)-(a+
21
51
)×b,

=ab+

21
51
a-ab-
21
51
b,

=

21
51
×(a-b),

=

21
51
×
17
11

=

7
11

判断题
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