角度的测量值比其补充值的两倍多21°。你如何找到每个角度的尺度?
53,127设x是角度补充的度量=> x'= 2x + 21因为两个角度是补充x + x'= 180 => x + 2x + 21 = 180 => 3x = 159 => x = 53 => x'= 127
在六天的时间内,外面的温度从76°F变为40°F。如果每天温度变化相同,那么每天的温度变化是多少? A. -6°F B. 36°F C. -36°F D. 6°F
D. 6 ^ @“F”找出温差。将差额除以六天。温差= 76 ^ @“F” - “40”^ @“F”=“36”^ @“F”每日温度变化=(“36”^ @“F”)/(“6天”)=“ 6 “^ @” F /天”
证明 ? Cos10°cos20°+ Sin45°Cos145°+ Sin55°Cos245°= 0
LHS = cos10cos20 + sin45cos145 + sin55cos245 = 1/2 [2cos10cos20 + 2sin45cos145 + 2sin55cos245] = 1/2 [cos(10 + 20)+ cos(20-10)+ sin(45 + 145)-sin(145-45) + sin(245 + 55)-sin(245-55)] = 1/2 [cos30 + cos10cancel(+ sin190)-sin100 + sin300cancel(-sin190)] = 1/2 [sin(90-30)+ cos10- sin(90 + 10)+ sin(360-60)] = 1/2 [取消(sin60)取消(+ cos10)取消(-cos10)取消(-sin60)] = 1/2 * 0 = 0 = RHS