If (sinx+cosx=a), then 1+2sinxcosx=a2
False
We are given sinx+cosx=a. We have to check if 1+2sinxcosx=a2. For that,
(sinx+cosx)2 = a2
sin2x+cos2x+2sinxcosx = a2
1+2sinxcosx = a2
Hence, if (sinx+cosx=a), then 1+2sinxcosx=a2
If k = sinx + cosx and a = sinx - cosx then k2 + a2 is independent of x