题目
已知a,b,c是△ABC的三边,a,b,c满足等式b2=(c+a)(c-a),且5b-4c=0,求sinA+sinB的值.
提问时间:2021-02-17
答案
∵b2=(c+a)(c-a),
∴b2=c2-a2,
即:a2+b2=c2,
∴△ABC是以c为斜边的Rt△ABC,
∵5b-4c=0,∴
=
,
设b=4k,则c=5k,
∴△ABC中,a=3k,
∴sinA+sinB=
+
=
+
=
+
=
.
∴b2=c2-a2,
即:a2+b2=c2,
∴△ABC是以c为斜边的Rt△ABC,
∵5b-4c=0,∴
b |
c |
4 |
5 |
设b=4k,则c=5k,
∴△ABC中,a=3k,
∴sinA+sinB=
a |
c |
b |
c |
3k |
5k |
4k |
5k |
3 |
5 |
4 |
5 |
7 |
5 |
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