Verified answer

a^2 - b^2 = (a - b)(a + b)

(x+a)^2-(y+b)^2=(x+y+1)*(x-y-5)

(x+a)^2-(y+b)^2 = (x + a + y + b)*(x + a - y - b) = (x+y + a+b)(x-y+a-b)

сравнивая с (x+y+1)*(x-y-5)

a+b= 1

a-b = -5

2a=-4

a=-2

b=3

a+2b = -2+2*3 = -2 + 6 = 4