已知cosA=cosQ乘以sinC,cosB=sinQ乘以sinC.求SINA的平方+SINB的平方+SINC的平方的值
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已知cosA=cosQ乘以sinC,cosB=sinQ乘以sinC.求SINA的平方+SINB的平方+SINC的平方的值?求详细步骤
![已知cosA=cosQ乘以sinC,cosB=sinQ乘以sinC.求SINA的平方+SINB的平方+SINC的平方的值](/uploads/image/z/17887802-50-2.jpg?t=%E5%B7%B2%E7%9F%A5cosA%3DcosQ%E4%B9%98%E4%BB%A5sinC%2CcosB%3DsinQ%E4%B9%98%E4%BB%A5sinC.%E6%B1%82SINA%E7%9A%84%E5%B9%B3%E6%96%B9%EF%BC%8BSINB%E7%9A%84%E5%B9%B3%E6%96%B9%EF%BC%8BSINC%E7%9A%84%E5%B9%B3%E6%96%B9%E7%9A%84%E5%80%BC)
注:sin^2(a)表示sin(a)的平方
sin^2(A) + sin^2(B) + sin^2(C) = 1 - cos^2(A) + 1 - cos^2(B) + sin^2(C)
= 2 - cos^2(A) - cos^2(B) + sin^2(C)
= 2 - (cosQ * sinC)^2 - (sinQ * sinC)^2 + sin^2(C)
= 2 - sin^2(C) * (cos^2(Q) + sin^2(Q)) + sin^2(C)
= 2 - sin^2(C) + sin^2(C)
= 2
sin^2(A) + sin^2(B) + sin^2(C) = 1 - cos^2(A) + 1 - cos^2(B) + sin^2(C)
= 2 - cos^2(A) - cos^2(B) + sin^2(C)
= 2 - (cosQ * sinC)^2 - (sinQ * sinC)^2 + sin^2(C)
= 2 - sin^2(C) * (cos^2(Q) + sin^2(Q)) + sin^2(C)
= 2 - sin^2(C) + sin^2(C)
= 2
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