Hello there, one of my text books follows that:

a2 = (c-bcosA)^2 + (bsinA)^2

leads to:

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!