а) x∈(-∞;4)∪(4;7)∪(7;+∞)
б) x/(x-4) - 5/(x-7)= 0
(x(x-7)-5(x-4))/(x-4)(x-7)=0
(x²-7x-5x+20)/(x-4)(x-7)=0
(x²-12x+20)/(x-4)(x-7)=0
в) x²-12x+20=0
D= 144-80= 64
x1= (12+8)/2= 10
x2= (12-8)/2= 2
Sin(A + <span>π) = -sinA
sin(A + 3</span>π/2) = sin(A + π + π/2) = -sin(A + <span>π/2) = -cosA
cos(3</span>π - A) = cos(2π + π - A) = cos(π - A) = -cosA
cos(<span>π/2 + A) = -sinA
-sinA/(-cosA) - cosA/(-sinA - 1) = sinA/cosA + cosA/(sinA + 1) =
= [sinA(sinA + 1) + cos</span>²A)]/(sinAcosA + cosA) =
(sin²A + cos²A + sinA)/(sinAcosA + cosA) = (1 + sinA)/cos(1 + sinA) =
= 1/cosA, чтд
График данного уравнения прилагается во вложении