標題:
Maths MC(need detailed steps)
發問:
1.) If four arithmatic means are inserted between 12 and 27, then the sum of the four arithmatic means is A. 78 B. 90 B. 105 D. 117 2.) sin^2 1度 + sin^2 3度+sin^2 5度+...+sin^2 87度+sin^2 89度= A. 22 B. 22.5 C. 44.5 D. 45
最佳解答:
1.) If four arithmatic means are inserted between 12 and 27, then the sum of the four arithmatic means is A. 78 B. 90 B. 105 D. 117 sol (12+27)*(4+2)/2=117 (D) 2.) sin^2 1度 + sin^2 3度+sin^2 5度+...+sin^2 87度+sin^2 89度= A. 22 B. 22.5 C. 44.5 D. 45 sol A=sin^2 1度 + sin^2 3度+sin^2 5度+...+sin^2 87度+sin^2 89度 A=sin^2 89度 + sin^2 87度+sin^2 85度+...+sin^2 3度+sin^2 1度 ------------------------------------------------------------------------------------ 2A=1+1+1+1....+1=1*(89+1)/2=45 A=22.5 (B)
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