Question

第六题第二问

Answer 1

（2）【sin（x+2h）-sinx】/2h=【2cos（x+h）sinh】/2h=cos(x+h)sinh/h
用和差化积的公式，一步就出来了

Answer 2

f(x+2h)=sin(x+2h)
sin(x+a)-sinx
=sin[(x+a/2)+a/2]-sin[x+a/2-a/2]
=sin(x+a/2)cosa/2+cos(x+a/2)sina/2-sin(x+a/2)cos(a/2)+cos(x+a/2)sin(a/2)
=2sin(a/2)cos(x+a/2)
f(x+2h)-f(x)/2h=sin(x+2h)-sin(x)/2h=(2sin(2h/2)cos(x+2h/2))/2h=cos(x+h*)sin(h)/h

追问

没看懂 能写出来么( ･᷄ὢ･᷅ )

追答

sin(x+2h)-sinx=sin(x+h+h)-sin(x+h-h)=sin(x+h)cosh+cos(x+h)sinh
-sin(x+h)cosh+cos(x+h)sinh
=2cos(x+h)sinh