launch+sb+into+sth

冯杰泰1343关于不定式做主语的、.、.、.,It is+adj.+for/of+sb+to do sth -
姬宜乔17110152366 ______ 形容词修饰物时用for It's difficult for me to study English.(指学英语难) 指人的性格,品格时用of It's kind of you to help me with English.(指我是善良的)

冯杰泰1343下面程序段的时间复杂度是 - s=0; for(i=0;i<m;i++) for(j=0;j<n;j+...
姬宜乔17110152366 ______[答案] 【解】两边平方 (3sinA+4cosB)^2=36 得9sin^2A +16cos^2B +24sinAcosB=36 ① (4sinB+3cosA)^2=1 得16sin^2B +9cos^2A +24sinBcosA=1 ② ①+ ② 得:(9sin^2A +9cos^2A) +(16cos^2B+ 16sin^2B) +24sinAcosB+24sinBcosA=37 即 9+16+...

冯杰泰1343三角函数证明题在△ABC中,r、R分别是△ABC的内接圆半径和外接圆半径,求证 :4sin(A/2)sin(B/2)sin(C/2)=r/R. -
姬宜乔17110152366 ______[答案] 由三角形ABC的面积为S=〔(a+b+c)r〕/2=(ab*sinC)/2,由正弦定理的,a/sinA=b/sinB=c/sinC=2R,则2Rr(sinA+sinB+sinC)/2=4R^2(sinA*sinB*sinC)/2,r/R=2(sinA*sinB*sinC)/(sinA+sinB+sinC) 那么下面证明2(sinA*sinB*sinC)/(sinA+sinB+sinC)=4sin(A/2)...

冯杰泰1343It's+adj.+of sb+to do sth是什么意思? -
姬宜乔17110152366 ______ 这是动词不定式的复合结构,请看例句: It is very nice of you to help me with my English. 您帮我学英语,您真是太好了.

冯杰泰1343求三角形三个角的正弦值和的最大正值? -
姬宜乔17110152366 ______[答案] sinA+sinB=2sin[(A+B)/2]*cos[(A-B)/2]≤2sin[(A+B)/2] 同理:sinA+sinB+sinC+sin[(A+B+C)/3]≤2sin[(A+B)/2]+2sin{[C+(A+B+C)/3]/2} ≤4sin{[(A+B)/2+[C+(A+B+C)/3]/2}/2=4sin[(A+B+C)/3] sinA+sinB+sinC≤3sin[(A+B+C)/3]=3√3/2.