(sinx-siny)/sin(x+y) = sin1/2(x-y)/sin1/2(x+y)还有这个sec(π/4+α)sec(π/4-α)=2sec2α

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(sinx-siny)/sin(x+y) = sin1/2(x-y)/sin1/2(x+y)还有这个sec(π/4+α)sec(π/4-α)=2sec2α
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(sinx-siny)/sin(x+y) = sin1/2(x-y)/sin1/2(x+y)还有这个sec(π/4+α)sec(π/4-α)=2sec2α
(sinx-siny)/sin(x+y) = sin1/2(x-y)/sin1/2(x+y)
还有这个sec(π/4+α)sec(π/4-α)=2sec2α

(sinx-siny)/sin(x+y) = sin1/2(x-y)/sin1/2(x+y)还有这个sec(π/4+α)sec(π/4-α)=2sec2α
sinx=sin[(x+y)/2]cos[(x-y)/2]+cos[(x+y)/2]sin[(x-y)/2]
siny=sin[(x+y)/2]cos[(x-y)/2]-cos[(x+y)/2]sin[(x-y)/2]
sinx-siny=2cos[(x+y)/2]sin[(x-y)/2]
sin(x+y)=2sin[(x+y)/2]cos[(x+y)/2]
所以(sinx-siny)/sin(x+y)=sin[(x-y)/2]/sin[(x+y)
sec(π/4+α)=1/cos(π/4+α)=1/(cosπ/4cosα-sinπ/4sinα)=(√2)/(cosα-sinα)
sec(π/4-α)=1/cos(π/4-α)=1/(cosπ/4cosα+sinπ/4sinα)=(√2)/(cosα+sinα)
所以sec(π/4+α)sec(π/4-α)=2/[(cosα)^2-(sinα)^2]=2/cos2α=2sec2α

证明sin(x+y)sin(x-y)=sinx-siny 证明sinx+cos(x+y)siny/cosx-sin(x+y)siny=tan(x+y) 为什么sinx*cosy-cosx*siny=sin(x-y) 求函数z=sinx+siny+sin(x+y)(0 存在sin( x -y) = sinX-sinY吗 sinx siny-sin(x y)如何化简 证明 [sin(2x+y)/sinx]-2cos(x+y)=siny/sinx 求证sin（2x+y)/sinx-2cos(x+y)=siny/sinx 求证：sin(2x+y)/sinx-2cos(x+y)=siny/sinx 证明sin(x+y)sin(x-y)=（sinx）^2-(siny）^2. 三角不等式证明证明sin(x+y)+sin(y+z)+sin(z+x)>sinx+siny+sinz+sin(x+y+z) 求下列导数：sin(x+y)=sinx+siny e^x+x=e^y+y 证明cosx(cosx-cosy)+sinx(sinx-siny)=2sin(x-y)/2 请问,如何证明sinx+siny=2*sin(x+y/2)*cos(x-y/2) 为什么sin（x+y) - sinx = 2cos(x+y/2)siny/2 求推导sinx-siny=2cos（(x+y)/2)sin((x-y)/2) 求证sinx+siny=2sin(x+y)/2*cos(x-y)/2 求证:sinx+siny=2sin(x+y)/2cos(x-y)/2