Question

快回复已知△ABC的三内角A,B,C所对边的长分别为a,b,c,设向量p=(a+c,b),q=(b-a,c-a),若p/

Answer 1

p//q----> (a+c)*(c-a) -b(b-a)=0

c^2-a^2-b^2 +ab=0------>a^2+b^2-c^2= ab

cosC = (a^2+b^2-c^2)/2ab= ab/2ab =1/2 ---->C=60度.

s=1/2 ac sinB =1/2 *c* 根号3/2 = 根号3/2

c=2

cosB =( a^2+b^2-c^2)/2ab= 1/2

(1+b^2 -4)/2b =1/2------>b=(1+根号13）/2

c/sinC= b/sinB-----