Зная что cosa = - 3\5, П\2 меньше a меньше П, найдите sin (  ( П\4 ) + a)

[latex]sina= \sqrt{1-cos^{2}a}\\sina= \sqrt{1-(- \frac{3}{5})^{2}}=\sqrt{1- \frac{9}{25}}= \sqrt{\frac{16}{25}}= \frac{4}{5} \\ sin( \frac{ \pi }{4}+a)=sin \frac{ \pi }{4}cosa+cos \frac{ \pi }{4}sina;\\ \frac{ \sqrt{2}}{2}*(- \frac{3}{5})+ \frac{ \sqrt{2}}{2}* \frac{4}{5}=- \frac{3 \sqrt{2}}{10}+ \frac{4 \sqrt{2}}{10}= \frac{ \sqrt{2}}{10}[/latex]

[latex]sin \alpha = \sqrt{1- cos \alpha ^{2} } = \sqrt{1- \frac{9}{25} } = \frac{4}{5} =0.8[/latex] [latex]sin( \pi /4+ \alpha ) =sin( \pi /4)cos( \alpha )+cos( \pi /4)sin( \alpha )[/latex] [latex] \frac{ \sqrt{2} }{2}*(- 0.6)+\frac{ \sqrt{2} }{2}*0.8=\frac{ \sqrt{2} }{2}*0.2=\frac{ \sqrt{2} }{2}* \frac{1}{5}=\frac{ \sqrt{2} }{10}[/latex]