Question

Упростить выражение:!!!

Answer 1

sin7b-sin11b=

2sin((7b-11b)/2)×cos((7b+11b)/2)=-2sin2b×cos9b=

-4sinb×cosb×cos9b=

cos10b-cos8b= -2sin((10b+8b)/2)×sin((10b-8b)/2)= -2sin9b×sinb

(sin7b-sin11b)/(cos10b-cos8b)=

(-4sinb×cosb×cos9b)/

(-2sin9b×sinb)=

2cosb×ctg9b.