请问:在三角形ABC中,内角A,B,C的对边a,b,c,已知a,b,c成等比数列,cosB=3/4在三角形ABC中,内角A,B,C的对边a,b,c,已知a,b,c成等比数列,cosB=3/41.求CotA+cotC的值 2.向量BA乘以向量BC=3/2,求a+c的值
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![请问:在三角形ABC中,内角A,B,C的对边a,b,c,已知a,b,c成等比数列,cosB=3/4在三角形ABC中,内角A,B,C的对边a,b,c,已知a,b,c成等比数列,cosB=3/41.求CotA+cotC的值 2.向量BA乘以向量BC=3/2,求a+c的值](/uploads/image/z/2501500-4-0.jpg?t=%E8%AF%B7%E9%97%AE%EF%BC%9A%E5%9C%A8%E4%B8%89%E8%A7%92%E5%BD%A2ABC%E4%B8%AD%2C%E5%86%85%E8%A7%92A%2CB%2CC%E7%9A%84%E5%AF%B9%E8%BE%B9a%2Cb%2Cc%2C%E5%B7%B2%E7%9F%A5a%2Cb%2Cc%E6%88%90%E7%AD%89%E6%AF%94%E6%95%B0%E5%88%97%2CcosB%EF%BC%9D3%EF%BC%8F4%E5%9C%A8%E4%B8%89%E8%A7%92%E5%BD%A2ABC%E4%B8%AD%2C%E5%86%85%E8%A7%92A%2CB%2CC%E7%9A%84%E5%AF%B9%E8%BE%B9a%2Cb%2Cc%2C%E5%B7%B2%E7%9F%A5a%2Cb%2Cc%E6%88%90%E7%AD%89%E6%AF%94%E6%95%B0%E5%88%97%2CcosB%EF%BC%9D3%EF%BC%8F41.%E6%B1%82CotA%2BcotC%E7%9A%84%E5%80%BC+2.%E5%90%91%E9%87%8FBA%E4%B9%98%E4%BB%A5%E5%90%91%E9%87%8FBC%EF%BC%9D3%EF%BC%8F2%2C%E6%B1%82a%EF%BC%8Bc%E7%9A%84%E5%80%BC)
请问:在三角形ABC中,内角A,B,C的对边a,b,c,已知a,b,c成等比数列,cosB=3/4在三角形ABC中,内角A,B,C的对边a,b,c,已知a,b,c成等比数列,cosB=3/41.求CotA+cotC的值 2.向量BA乘以向量BC=3/2,求a+c的值
请问:在三角形ABC中,内角A,B,C的对边a,b,c,已知a,b,c成等比数列,cosB=3/4
在三角形ABC中,内角A,B,C的对边a,b,c,已知a,b,c成等比数列,cosB=3/4
1.求CotA+cotC的值 2.向量BA乘以向量BC=3/2,求a+c的值
请问:在三角形ABC中,内角A,B,C的对边a,b,c,已知a,b,c成等比数列,cosB=3/4在三角形ABC中,内角A,B,C的对边a,b,c,已知a,b,c成等比数列,cosB=3/41.求CotA+cotC的值 2.向量BA乘以向量BC=3/2,求a+c的值
a,b,c成等比数列
b²=ac
b²=a²+c²-2ac*(3/4)
a²+c²=5ac/2
(1) cotA+cotC
=cosA/sinA+cosC/sinC
=(cosAsinC+cosCsinA)/sinAsinC
=sinB/sinAsinCa²+c²=5ac/2a²+c²=5ac/2
=sin²B/(sinAsinBsinC)
=b²/(acsinB)
=1/sinB
=4/√7
=4√7/7
(2)
BA.BC=3/2
ca*cosB=3/2
ac=2
又因为
a²+c²=5ac/2
(a+c)²=9ac/2=9
所以 a+c=3
a,b,c成等比数列
b²=ac
b²=a²+c²-2ac*(3/4)
a²+c²=5ac/2
(1) cotA+cotC
=cosA/sinA+cosC/sinC
=(cosAsinC+cosCsinA)/sinAsinC
=sinB/sinAsinCa²+c²...
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a,b,c成等比数列
b²=ac
b²=a²+c²-2ac*(3/4)
a²+c²=5ac/2
(1) cotA+cotC
=cosA/sinA+cosC/sinC
=(cosAsinC+cosCsinA)/sinAsinC
=sinB/sinAsinCa²+c²=5ac/2a²+c²=5ac/2
=sin²B/(sinAsinBsinC)
=b²/(acsinB)
=1/sinB
=4/√7
=4√7/7
(2)
BA.BC=3/2
ca*cosB=3/2
ac=2
又因为
a²+c²=5ac/2
(a+c)²=9ac/2=9
所以 a+c=3
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