Вычислите (tg a-ctd a) : (sin a - cos a), если sin a+ cos a=1,2

Решите задачу:

$(tga-ctga):(sina-cosa)=(\frac{sina}{cosa}-\frac{cosa}{sina}):(sina-cosa)=\\\\=\frac{sin^2a-cos^2a}{sina\cdot cosa}\cdot \frac{1}{sina-cosa}=\frac{(sina-cosa)(sina+cosa)}{sina\cdot cosa\cdot (sina-cosa)}=\frac{sina+cosa}{sina\cdot cosa}=\\\\=\frac{1,2}{sina\cdot cosa}=\frac{1,2}{0,22}=\frac{120}{22}=\frac{60}{11}=5\frac{5}{11}\\\\\\\star \; \; sina+cosa=1,2\\\\(sina+cosa)^2=1,44\\\\sin^2a+2sina\cdot cosa+cos^2a=1,44\\\\1+2sina\cdot cosa=1,44\\\\2sina\cdot cosa=1,44-1\\\\2sina\cdot cosa=0,44\\\\sina\cdot cosa=0,22$