Explicación paso a paso:
sen²b+cos²b=1
(senb+cosb)²=1+2senb×cosb
sen²b+2senb×cosb+cos²b=1+2senb×cosb
(sen²b+cos²b)+2senb×cosb= 1+2senb×cosb
1+2senb×cosb=1+2senb×cosb
