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已知sin^4A+Cos^4A=5/9,求sin2A的值

sin^4a+cos^4a=(sin^2a+cos^2a)^2-2sin^2acos^2a=5/9 1-2sin^2acos^2a=5/9 sin^2acos^2a=2/9 sin^2acos^2a=(sin2a)^2/4=2/9 (sin2a)^2=8/9 sin2a=±2根号2/3

cos2A=3/5 (sin2A)^2 = 1- 9/25 = 16/25 (sinA)^4+(cosA)^2 =[(sinA)^2+(cosA)^2]^2 - 2(sinAcosA)^2 =1- (1/2)(sin2A)^2 =1- (1/2)(16/25) =17/25

sin^4a+cos^4a =(sin²a+cos²a)²-2sin²acos²a =1-2(sinacosa)²=5/9 (sinacosa)²=2/9 第三象限 sina

sin^4A+cos^4A=(+cos^2A)-2sin^2Acos^2A=1-1/2 sin^2A=1-1/2(1/4)^2=31/32

2倍角公式啊cos4a=1-2(sin2a)^2

sin4a-cos4a=sin²a-cos²a, 这里,sin4a中的4是4次方,(sina)^4,不是a*4 这样写清晰一些: (sina)^4-(cosa)^4 =[(sina)^2+(cosa)^2]*[(sina)^2-(cosa)^2] (sina)^2+(cosa)^2=1 =(sina)^2-(cosa)^2 这样就理解了吧!

cos2a=±√(1-9/25)=±4/5; 所以sin4a=2sin2acos2a=±2×3/5×4/5=±24/25; 请采纳 如果你认可我的回答,敬请及时采纳, ~如果你认可我的回答,请及时点击【采纳为满意回答】按钮 ~~手机提问的朋友在客户端右上角评价点【满意】即可。 ~你的采纳是我...

cos2a=cos^2a-sin^2a=1-2sin^a=4/5 ,sin^2a=1/10, cos^a=9/10 (cos^2a-sin^2a)^2=16/25=cos^4a+sin^4a-2cos^2asin^2a cos^4a+sin^4a=16/25+2cos^2asin^2a=16/25+9/50=41/50

sin2a-cos4a =sin2a - 1 + 2sin²2a sina + cosa =m sin²a +cos²a + 2sinacosa =m² 1+2sinacosa =m² sin2a = m² -1 所以: sin2a-cos4a =sin2a - 1 + 2sin²2a =m²-1 -1 + 2 m^4 + 4m² +2 =2m^4 + 5...

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