【高一数学】若向量a+向量b+向量c=0,且|a|=3,|b|=3,|c|=4,则a*b+b*c+a*c=____1.若向量a+向量b+向量c=0,且|a|=3,|b|=3,|c|=4,则a*b+b*c+a*c=____(注:题中a,b,c均为向量);2.设sina+cosb=1/5,则sin^3a+cos^3a=____;3.若a+b+c=
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![【高一数学】若向量a+向量b+向量c=0,且|a|=3,|b|=3,|c|=4,则a*b+b*c+a*c=____1.若向量a+向量b+向量c=0,且|a|=3,|b|=3,|c|=4,则a*b+b*c+a*c=____(注:题中a,b,c均为向量);2.设sina+cosb=1/5,则sin^3a+cos^3a=____;3.若a+b+c=](/uploads/image/z/6836858-26-8.jpg?t=%E3%80%90%E9%AB%98%E4%B8%80%E6%95%B0%E5%AD%A6%E3%80%91%E8%8B%A5%E5%90%91%E9%87%8Fa%2B%E5%90%91%E9%87%8Fb%2B%E5%90%91%E9%87%8Fc%3D0%2C%E4%B8%94%7Ca%7C%3D3%2C%7Cb%7C%3D3%2C%7Cc%7C%3D4%2C%E5%88%99a%2Ab%2Bb%2Ac%2Ba%2Ac%3D____1.%E8%8B%A5%E5%90%91%E9%87%8Fa%2B%E5%90%91%E9%87%8Fb%2B%E5%90%91%E9%87%8Fc%3D0%2C%E4%B8%94%7Ca%7C%3D3%2C%7Cb%7C%3D3%2C%7Cc%7C%3D4%2C%E5%88%99a%2Ab%2Bb%2Ac%2Ba%2Ac%3D____%EF%BC%88%E6%B3%A8%EF%BC%9A%E9%A2%98%E4%B8%ADa%2Cb%2Cc%E5%9D%87%E4%B8%BA%E5%90%91%E9%87%8F%EF%BC%89%EF%BC%9B2.%E8%AE%BEsina%2Bcosb%3D1%2F5%2C%E5%88%99sin%5E3a%2Bcos%5E3a%3D____%EF%BC%9B3.%E8%8B%A5a%2Bb%2Bc%3D)
【高一数学】若向量a+向量b+向量c=0,且|a|=3,|b|=3,|c|=4,则a*b+b*c+a*c=____1.若向量a+向量b+向量c=0,且|a|=3,|b|=3,|c|=4,则a*b+b*c+a*c=____(注:题中a,b,c均为向量);2.设sina+cosb=1/5,则sin^3a+cos^3a=____;3.若a+b+c=
【高一数学】若向量a+向量b+向量c=0,且|a|=3,|b|=3,|c|=4,则a*b+b*c+a*c=____
1.若向量a+向量b+向量c=0,且|a|=3,|b|=3,|c|=4,则a*b+b*c+a*c=____
(注:题中a,b,c均为向量);
2.设sina+cosb=1/5,则sin^3a+cos^3a=____;
3.若a+b+c=0,且|a|=3,|b|=3,|c|=4,则a*b+b*c+a*c=_____
(注:题中a,b,c,0均为向量)
【高一数学】若向量a+向量b+向量c=0,且|a|=3,|b|=3,|c|=4,则a*b+b*c+a*c=____1.若向量a+向量b+向量c=0,且|a|=3,|b|=3,|c|=4,则a*b+b*c+a*c=____(注:题中a,b,c均为向量);2.设sina+cosb=1/5,则sin^3a+cos^3a=____;3.若a+b+c=
唉,可惜我传不了图片啊.
第一题,因为a+b+c=0,所以两边完全平方得:a^2+b^2+c^2+2ab=2ac+2bc=0,往下会算了吧?答案是-17
第二题,题错了吧?应该是sina+cosa=1/5.根据立方差公式sin^3a+cos^3a=(sina+cosb)*(sin^2a+cos^2a-sina*cosa)
(sina+cosb)^2=sin^2a+cos^2a+2sina*cosb=1/25;所以sina*cosb=-12/25往下回了吧?答案是:37/125
第二题做不了!
—17
-17