設(shè)k∈Z,化簡sin(kπ?α)cos[(k?1)π?α]sin[(k+1)π+α]cos(kπ+α)的結(jié)果是( ?。?A.-1 B.當(dāng)k為偶數(shù)時,值為-1;當(dāng)k為奇數(shù)時,值為1 C.1 D.當(dāng)k為奇數(shù)時,值為-1;當(dāng)k為偶數(shù)時,值為1
設(shè)k∈Z,化簡
sin(kπ?α)cos[(k?1)π?α] |
sin[(k+1)π+α]cos(kπ+α) |
的結(jié)果是( ?。?br/>A. -1
B. 當(dāng)k為偶數(shù)時,值為-1;當(dāng)k為奇數(shù)時,值為1
C. 1
D. 當(dāng)k為奇數(shù)時,值為-1;當(dāng)k為偶數(shù)時,值為1
優(yōu)質(zhì)解答
∵k∈Z,
∴當(dāng)k為偶數(shù)時,原式=
=-1;
當(dāng)k為奇數(shù)時,原式=
=-1;
綜上所述,k∈Z,
sin(kπ?α)cos[(k?1)π?α] |
sin[(k+1)π+α]cos(kπ+α) |
=-1.
故選A.
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