(sinA-sinB)(sinA+sinB)推出sin(A+B)sin(A-B)
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(sinA-sinB)(sinA+sinB)推出sin(A+B)sin(A-B)(sinA-sinB)(sinA+sinB)推出sin(A+B)sin(A-B)(sinA-sinB)(sinA+sin
(sinA-sinB)(sinA+sinB)推出sin(A+B)sin(A-B)
(sinA-sinB)(sinA+sinB)推出sin(A+B)sin(A-B)
(sinA-sinB)(sinA+sinB)推出sin(A+B)sin(A-B)
(sina-sinb)(sina+sinb)
=(sina)^2-(sinb)^2 (平方差公式)
=(1-cos2a)/2-(1-cos2b)/2 (二倍角公式)
=1/2*(cos2b-cos2a) (合并)
=1/2*{cos[(a+b)-(a-b)]-cos[(a+b)+(a-b)]} (化角 2a=(a+b)+(a-b) ,2b=(a+b)-(a-b))
=1/2*{[cos(a+b)cos(a-b)+sin(a+b)sin(a-b)]-[cos(a+b)cos(a-b)-sin(a+b)sin(a-b)]} (和角公式)
=1/2*2sin(a+b)sin(a-b) (合并)
=sin(a+b)sin(a-b) (约分)