А15=-9.1*2.5(15-1)=-9.1*2.5*14=-9.1*35=-318.5
а)(x+4)^2=(x^2+8x+16)
б)(3в-c)^2=(9в^2-6вc+с^2)
в)(2y+5)(2y-5)=4y^2-25
г)(y^2-x)(y^2+x)=y^4-x^2
прости что смогла
Cosˇ2(a) + cosˇ2(a)/sinˇ2(a) - 1/sinˇ2(a)=
=cosˇ2(a)+ (cosˇ2(a)-1)/sinˇ2(a)=cosˇ2(a)- (1-cosˇ2(a))/sinˇ2(a)=
=cosˇ2(a)-sinˇ2(a)/sinˇ2(a)=cosˇ2(a)-1=-(1-cosˇ2(a))=-sinˇ2(a)