The Student Room Group
Reply 1
To prove any identity, start with one side and work your way logically to the other. Don't try to simplify both sides.
Reply 2
Try writing tan2x=sin2xsec2x and proceeding from there.
prove: tan2xsecx = 2sinxsec2x

tan2x.secx = sin2x/(cos2x.cosx) = (2sinxcosx)/(cos2xcosx) = 2sinx/(cos2x) = 2sinx.sec2x
Reply 4
= sin(2x)sec(x)sec(2x)
= 2sin(x)cos(x)sec(x)sec(2x)
= 2sin(x)sec(2x)
Reply 5
Reply 6
thanksss guys! makes sense now :smile: much much much MUCHHH appreciated!!!