Use: (a-b)^2=a^2-2.a.b+b^2 so you get:
Hello there, one of my text books follows that:
a2 = (c-bcosA)^2 + (bsinA)^2
a^2 = c2 -2cb cosA +b2Cos2A +b2sin2A
Please can someone please help as this is doing my head in! many thanks
i start by expanding out the brackets of the first term and distributing, but getting confused.. where does the -2cb come from!? ... thanks in advance!