Помогите срочно с номером 124,126,131(2,4)

131 [tex]cos ^{2} \frac{pi}{8}-sin^{2} \frac{pi}{8}=cos2* \frac{pi}{8}=cos \frac{pi}{4}= \frac{ \sqrt{2} }{2} " alt="2cos ^{2}a=1+cos2a 1+cos2a-cos2a=1 124 2 [tex]cos ^{2} \frac{pi}{8}-sin^{2} \frac{pi}{8}=cos2* \frac{pi}{8}=cos \frac{pi}{4}= \frac{ \sqrt{2} }{2} " align="absmiddle" class="latex-formula">
126 2 $sin ^{2}a= \sqrt{1-cos^{2}a } = \sqrt{1-(- \frac{4}{5} ) ^{2} } = \sqrt{1- \frac{16}{25} } = \sqrt{ \frac{25-16}{25} } = \sqrt{ \frac{9}{25} } = \frac{3}{5}$
sin2a=2sinacosa= $2* \frac{3}{5}*(- \frac{4}{5} )= \frac{24}{25}$
131 2 $(sina-cosa) ^{2} =sin ^{2}a-2sinacosa+cos^{2}a= 1-sin2a$