sin(kπ-α)•cos(kπ+α)∕sin[(k+1)π+α]•cos[(k+1)π-α]=1.
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sin(kπ-α)•cos(kπ+α)∕sin[(k+1)π+α]•cos[(k+1)π-α]=1.
证明:
左边=sina*(-cosa)/[-sina*(-cosa)]=-1=右边.
得证.
k为奇数
sin(kπ-α)•cos(kπ+α)∕sin[(k+1)π+α]•cos[(k+1)π-α]
=sina*(-cosa)/sina*cosa
=-1
k为偶数
sin(kπ-α)•cos(kπ+α)∕sin[(k+1)π+α]•cos[(k+1)π-α]
=-sina*cosa/(-sina)*(-cosa)
=-1