Question

17题怎么写？？？具体过程？？？

Answer 1

(1)btanA=(2c-b)tanB
sinBtanA=(2sinC-sinB)tanB
sinBsinA/cosA=(2sinC-sinB)sinB/cosB
sinA/cosA=(2sinC-sinB)/cosB
sinAcosB=(2sinC-sinB)cosA
sinAcosB=2sinCcosA-sinBcosA
sinAcosB+sinBcosA=2sinCcosA
sin(A+B)=2sinCcosA
sin(π-C)=2sinCcosA
sinC=2sinCcosA
而0<C<π，∴sinC≠0，∴1=2cosA
∴cosA=1/2，而0<A<π，∴A=π/3
(2)a²=b²+c²-2bccosA，∴9=4+c²-2c
∴c²-2c-5=0，而c>0，∴c=1+√6
∴S△ABC=1/2*bc*sinA=1/2*2*(1+√6)*√3/2=(√3+3√2)/2

望采纳

Answer 2