z=cosA+isinA
the Moivre formula
zn=cosnA+isinnAz−n=zn1=cosnA+isinnA1==(cosnA+isinnA)(cosnA−isinnA)cosnA−isinnA=cosnA−isinnA
1)
zn+z−n==cosnA+isinnA+cosnA−isinnA==2cosnAzn−z−n==cosnA+isinnA−cosnA+isinnA==2isinnA
2)
z+z−1=2cosA2cosA=(z+z1)(2cosA)n=(z+z1)n2ncosnA=(z+z1)nz−z−1=2isinA2isinA=(z−z1)(2isinA)n=(z−z1)n(2i)nsinnA=(z−z1)n
3)
sinnA=(2i)n(z−z−1)nsin7A=(2i)7(z−z−1)7=27i71(z7−7z6z−1++21z5z−2−35z4z−3+35z3z−4−21z2z−5++7zz−6−z−7)==128(−i)1(z7−z−7−7(z5−z−5)++21(z3−z−3)−35(z−z−1))==128(−i)i(2isin7A−7⋅2isin5A++21⋅2isin3A−35⋅2isinA)=−128i2i(sin7A−−7sin5A+21sin3A−35sinA)==−641(sin7A−7sin5A+21sin3A−35sinA)
i7=i4⋅i3=1⋅(−i)=−ii4=(i2)2=(−1)2=1i3=i2⋅i=−1⋅i=−i
4)
cosnA=2n(z+z−1)ncos3A=23(z+z−1)3=81(z3+3z2z−1++3zz−2+z−3)==81(z3+z−3+3(z+z−1)==81(2cos3A+3⋅2cosA)==41(cos3A+3cosA)sinnA=(2i)n(z−z−1)nsin4A=(2i)4(z−z−1)4=161(z4−4z3z−1++6z2z−2−4zz−3+z−4)==161(z4+z−4−4(z2+z−2)+6)==161(2cos4A−4⋅2cos2A+6)==81(cos4A−4cos2A+3)
5)
4x=cos3A+3cosAcos3A=41(cos3A+3cosA)cos3A=4cos3A−3cosA4x=4cos3A−3cosA+3cosAx=cos3A
4y=3sinA−sin3Asin3A=(2i)3(z−z−1)3=−8i1(z3−3z2z−1++3zz−2−z−3)==−8i1(z3−z−3−3(z−z−1)==−8i1(2isin3A−3⋅(2i)sinA)==−41(sin3A−3sinA)sin3A=3sinA−4sin3A4y=3sinA−3sinA+4sin3Ay=sin3A
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