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(tanA•tanB)/(tanC(tanA+tanB))……分子分母同乘以cosAcosB可得下式
=sinAsinB/((sinAcosB+cosAsinB)tanC)
=sinAsinB/(tanCsin(A+B))
=sinAsinBcosC/(sinCsinC)
=sinAsinB/(sinCsinC)*[(a^2+b^2-c^2)/(2ab)]
=[sinA/sinC]*[ sinB/sinC] *[(a^2+b^2-c^2)/(2ab)]
=(a/c)*(b/c) *[(a^2+b^2-c^2)/(2ab)]
=(a^2+b^2-c^2)/(2c^2)
=(2011 c^2-c^2)/(2c^2)
=1005.
=sinAsinB/((sinAcosB+cosAsinB)tanC)
=sinAsinB/(tanCsin(A+B))
=sinAsinBcosC/(sinCsinC)
=sinAsinB/(sinCsinC)*[(a^2+b^2-c^2)/(2ab)]
=[sinA/sinC]*[ sinB/sinC] *[(a^2+b^2-c^2)/(2ab)]
=(a/c)*(b/c) *[(a^2+b^2-c^2)/(2ab)]
=(a^2+b^2-c^2)/(2c^2)
=(2011 c^2-c^2)/(2c^2)
=1005.
1年前
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