没灵魂的妖精
幼苗
共回答了23个问题 举报
8, [cos(75)]^2+[sin(75)]^2+cos(15)sin(15)=1+1/2sin(30)=1+1/4=5/4. c. 5/4
9, 0=(2a+2b)(ka-b)=2k|a|^2+ab(2k-2)-2|b|^2=4k-6,k=3/2. a. 3/2
10, tan(A)+tan(B)=-8/3, tan(A)tan(B)=-1/3, tan(C)=tan(180-A-B)=-tan(A+B)=-[tan(A)+tan(B)]/[1-tan(A)tan(B)]=(8/3)/[1+1/3]=8/4=2
1年前
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