sinx+cosx=-1的解集是?

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sinx+cosx=-1的解集是?
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sinx+cosx=-1的解集是?
sinx+cosx=-1的解集是?

sinx+cosx=-1的解集是?
我给出2种解法:
解法1:
sinx+cosx=-1
两边平方得:
(sinx)²+(cosx)²+2sinxcosx=1
1+2sinxcosx=1
sinxcosx=0
sinx=0或cosx=0
1)当sinx=0时cosx=-1,此时x=2kπ-π,k∈Z
2)当cosx=0时sinx=-1,此时x=2kπ-π/2,k∈Z.
解法2:
∵sinx+cosx=√2sin(x+π/4)=-1
∴sin(x+π/4)=-√2/2
∴x+π/4=2kπ-3π/4或x+π/4=2kπ-π/4,k∈Z
∴x=2kπ-π或x=2kπ-π/2,k∈Z

sinx + cosx
=√2 *[(√2/2)*sinx + (√2/2)*cosx]
=√2 *[cos45°*sinx + sin45°*cosx]
=√2 *sin(45°+ x) = -1
sin(45°+ x) = -√2/2 = sin(-45°)
所以,
45°+ x = -45°+ n * 360°或 45°+ x = -135°+ n * 360° 注:n 为整数
x = n * 360°- 90°或 x = n * 360°- 180°