=(sinA+sinB)(sinA-sinB)
=(sinA+sinB)(sinA-sinB)
=2sin((A+B)/2)cos((A-B)/2)*2Cos((A+B)/2)Sin((A-B)/2)
=2sin((A+B)/2)Cos((A+B)/2)*2Sin((A-B)/2)cos((A-B)/2)
=sin(A+B)sin(A-B)本回答被提问者采纳
如何证明sinA2-sinB2=sin(A-B)*sin(A+B)
sinA2-sinB2=(sinA+sinB)(sinA-sinB)=(sinA+sinB)(sinA-sinB)=2sin((A+B)\/2)cos((A-B)\/2)*2Cos((A+B)\/2)Sin((A-B)\/2)=2sin((A+B)\/2)Cos((A+B)\/2)*2Sin((A-B)\/2)cos((A-B)\/2)=sin(A+B)sin(A-B)
如何证明sinA2-sinB2=sin(A-B)*sin(A+B)
sinA2-sinB2 =(sinA+sinB)(sinA-sinB)=(sinA+sinB)(sinA-sinB)=2sin((A+B)\/2)cos((A-B)\/2)*2Cos((A+B)\/2)Sin((A-B)\/2)=2sin((A+B)\/2)Cos((A+B)\/2)*2Sin((A-B)\/2)cos((A-B)\/2)=sin(A+B)sin(A-B)
sin2A-sin2B=2sin(A-B)cos(A+B)是怎么出来的
2A=(A＋B)＋(A－B)，则：sin2A=sin[(A＋B)＋(A－B)]=sin(A＋B)cos(A－B)＋cos(A＋B)sin(A－B) ---(1)2B=(A＋B)－(A－B)，则：sin2B=sin[(A＋B)－(A－B)]=sin(A＋B)cos(A－B)－cos(A＋B)sin(A－B) ---(2)(1)＋(2)，得：sin2A＋sin2B=2sin(A＋...
解三角形中。。。sinA的平方-sinB的平方为什么等于sin(A+B)sin(A-B)
=[2sin(A-B)\/2*cos(A-B)\/2]*[2cos(A+B)\/2*sin(A+B)\/2] 二倍角公式 =sin(A+B)*sin(A-B).
如何证明sin(A-B)*sin(A+B)=sinA⊃2;-sinB⊃2;
左边用积化和差公式=(cos2B-cos2A)\/2=(1-2sinB^2-1+2sinA^2)\/2=sinA^2-sinB^2
此式求证明sin(a+b)sin(a-b)=sin2a-sin2b 2代表的是平方
sin(a+b)=sinacosb+sinbcosa sin(a+b)=sinacosb-sinbcosa sin(a+b)sin(a-b)=(sin²acos²b-sin²bcos²a)=[sin²a(1-sin²b)-sin²b(1-sin²a)]=sin²a-sin²b
为什么sin2A+sin2B=sin2C得sin(A+B)cos(A-B)=2sinCcosC
sin2A+sin2B=sin2C得sin(A＋B)cos(A－B)=2sinCcosC 答：因为 sin(A＋B)=sinAcosB+sinBcosA cos(A－B)=cosAcosB+sinAsinB sin(A＋B)cos(A－B)=(sinAcosB+sinBcosA)(cosAcosB+sinAsinB)整理得 = sin2A+sin2B
已知sin2A-sin2B=0,问为什么cos(A+B)sin(A-B)=0
首先说明第一个回答错误 已知sin2A-sin2B=0,问为什么cos(A+B)sin(A-B)=0 解：sin2A=sin[(A+B)+(A-B)]=sin(A+B)cos(A-B)+cos(A+B)sin(A-B) ① sin2B=sin[(A+B)-(A-B)]=sin(A+B)cos(A-B)-cos(A+B)sin(A-B) ② ①-②得到sin2A-sin2B =2cos(A+B)...
证明SIN(A+B)的平方-2SINBCOSASIN(A+B)=SINA的平方-SINB的平方
sin^2(a+b)-2sinbXcosaXsin(a+b)=(sina*cosb+cosa*sinb)^2-2sinbXcosaXsin(a+b)=(sina*cosb)^2+(cosa*sinb)^2+2*(sina*cosb*cosa*sinb)-2sinbXcosaXsin(a+b)=(sina*cosb)^2+(cosa*sinb)^2+2*(sina*cosb*cosa*sinb)-2sinbXcosaX*(sina*cosb+cosa*sinb)=(sina*cosb)^...
△ABC 中,(a2+b2)sin(A-B)=(a2-b2)sin(A+B)判断三角形形状
简单分析一下，详情如图所示
