5(а-3b)-(7a+3b)=-2a-18b=0=0
tg(a+b)=(tga+tgb)/(1-tgatgb) = (1/3-2)/(1-1/3*(-2))=(-5/3)/(1+2/3) = (-5/3)/(5/3) = -1
ctg(a-b)=1/tg(a-b)=(1+tgatgb)/(tga-tgb) = (1+1/3*(-2))/(1/3+2) = (1-2/3)/( 7/3) = (1/3)/(7/3)=1/7
4-3y дробь y+4 :(4y-16-y^+4y+y^+4y дробь y^-4y+4y-16)= 4-3y добь y+4 :(12y-16 дробь
y^-16) = 4-3y дробь y+4 *y^-16 дробь 12y-16= 4-3y дробь y+4*(y-4)(y+4) дробь 4(3y-4)=
4-3y дробь y+4*(y-4)(y+4) дробь -4(4-3y)=-y-4 дробь 4