(cos(4次方)派/8)-(sin(4次方)派/8)等于多少?
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(cos(4次方)派/8)-(sin(4次方)派/8)等于多少?
(cos(4次方)派/8)-(sin(4次方)派/8)等于多少?
(cos(4次方)派/8)-(sin(4次方)派/8)等于多少?
(cosπ/8)^4-(sinπ/8)^4
=[(cosπ/8)^2+(sinπ/8)^2]*[(cosπ/8)^2-(sinπ/8)^2]
=1*cos(π/4)
=2分之根号2
(cosπ/8)^4-(sinπ/8)^4
=[(cosπ/8)^2+(sinπ/8)^2][(cosπ/8)^2-(sinπ/8)^2]
=1×cos(2×π/8)
=cosπ/4
=√2/2