已知tana=3,sin^2a+sinacosa+2cos^2a

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已知tana=3,sin^2a+sinacosa+2cos^2a已知tana=3,sin^2a+sinacosa+2cos^2a已知tana=3,sin^2a+sinacosa+2cos^2a(sin

已知tana=3,sin^2a+sinacosa+2cos^2a
已知tana=3,sin^2a+sinacosa+2cos^2a

已知tana=3,sin^2a+sinacosa+2cos^2a
(sina)^2+sinacosa+2(cosa)^2
=1+ sinacosa+ (cosa)^2
= 1+ ( sina + cosa)/{ 1/cosa}
= 1+ ( tana + 1)/ {1/(cosa)^2}
= 1+ (3+1)/ (10) ( cosa = 1/√10)
= 7/5


原式=2sinacosa+sinacosa+2cos²a-2sin²a
=(3sinacosa+2cos²a-2sin²a)÷(sin²a+cos²a)
=(3tana+2-2tan²a)÷(tan²a+1)
=(9+2-18)÷(9+1)
=-0.7

sina/cosa=3 sin^a+cos^a =1推出cosa=+-(根号10)/10 sin=+-(3根号10)/10
sinacosa=3/10
sin^2a+sinacosa+2cos^2a =1+ sinacosa+ (cosa)^2=1+3/10+1/10=7/5