计算:(1)2(2cos45°-1)+(4-5π)0-(2-1)-1(2)先化简,再求值.x-5x2-9÷x2-2x-15x2+6x+9+1x-3,其中x=3+2.-数学

题目简介

计算:(1)2(2cos45°-1)+(4-5π)0-(2-1)-1(2)先化简,再求值.x-5x2-9÷x2-2x-15x2+6x+9+1x-3,其中x=3+2.-数学

题目详情

计算:(1)
2
(2cos45°-1)+(4-5π)0-(
2
-1)-1

(2)先化简,再求值.
x-5
x2-9
÷
x2-2x-15
x2+6x+9
+
1
x-3
,其中x=
3
+2
题型:解答题难度:中档来源:不详

答案

(1)原式=
2
(2×
2
2
-1)+1-class="stub"1
2
-1

=
2
2
-1)+1-
2
-1
=2-
2
+1-
2
-1
=2-2
2

(2)原式=class="stub"x-5
(x+3)(x-3)
×
(x+3)2
(x+3)(x-5)
+class="stub"1
x-3

=class="stub"1
x-3
+class="stub"1
x-3

=class="stub"2
x-3

∵x=
3
+2,
∴原式=class="stub"2
x-3
=class="stub"2
3
+2-3
=class="stub"2
3
-1
=
3
+1

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