f(x)
=m.n-1
=(2cos(x/2),1).(sin(x/2),1)-1
=2cos(x/2)(sin(x/2)+1-1
=sinx
-1cosB=4/5
f(C)
=sinC
= sin(A+B)
= sinAcosB+cosAsinB
=(5/13)(4/5)+(12/13)(3/5)
=56/65
f(x)
=m.n-1
=(2cos(x/2),1).(sin(x/2),1)-1
=2cos(x/2)(sin(x/2)+1-1
=sinx
-1cosB=4/5
f(C)
=sinC
= sin(A+B)
= sinAcosB+cosAsinB
=(5/13)(4/5)+(12/13)(3/5)
=56/65