问题
解答题
计算. (1)1+4
(2)(
|
答案
(1)1+4
+71 6
+101 12
+131 20
+161 30
+191 42
+221 56
+251 72
,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
=a,20 41
+18 21
+19 31
=b,则a-b=20 41
+17 11
+18 21
+19 31
-(20 41
+18 21
+19 31
)=20 41
,那么:17 11
(
+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+
)-(a+21 51
)×b,21 51
=ab+
a-ab-21 51
b,21 51
=
×(a-b),21 51
=
×21 51
,17 11
=
.7 11