Question

решите плиз 16,17 и 18

Answer 1

16
$cos^{2} a+4* frac{1-cos6a}{2} * frac{1+cos6a}{2}$
$cos^{2} 6a+(1-cos6a)(1+cos6a)= cos^{2}6a+(1-cos^{2}6a) =1$
17
$frac{1-(cos^{2}a- sin^{2} a)+2sin a*cos a }{cos a+sin a}$
$frac{ sin^{2}a+ sin^{2} a+2sin a*cos a }{sin a+cos a} = frac{2sin a(sin a+cos a}{sin a+cos a} =2 sin a$
18
$( cos^{2}a- sin^{2} a)* frac{1}{cos ^{2}a } -1=1- tg^{2} a-1=-tg^{2} a$