Given A+B+C=180o,sin2A+sin2B+sin2CsinA+sinB+sinC=ksinA2sinB2sinC2
.....(1)
Consider,
sin2A+sin2B+sin2CsinA+sinB+sinC
We have
sin2A+sin2B+sin2C=4sinAsinBsinC
and sinA+sinB+sinC=4cos(A2)cos(B2)cos(C2)
=4sinAsinBsinC4cos(A2)cos(B2)cos(C2)
=8sin(A2)sin(B2)sin(C2)
Put this value in (1), we get
⇒k=8