Question

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

Answer 1

131 $2cos ^{2}a=1+cos2a 1+cos2a-cos2a=1    124  2 <strong></strong>[tex]cos ^{2} frac{pi}{8}-sin^{2} frac{pi}{8}=cos2* frac{pi}{8}=cos frac{pi}{4}= frac{ sqrt{2} }{2}$
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$(sina-cosa) ^{2} =sin ^{2}a-2sinacosa+cos^{2}a= 1-sin2a$