Question

数学余玹定理已知三角形ABC,三边长分别为a=2 b=3 c=根号7.求三角形面积.

Answer 1

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

=(4+9-7)/(2*2*3)

=6/12=1/2

∵C0

sinC=√(1-cos^2C)=√3/2

S△ABC=1/2*a*bsinC=1/2*2*3*√3/2=3√3/2