Verified answer

a + b = 0  ⇒  b = - a

a² + 6ab + 5b² + 1 = a² + 6a * (- a) + 5a² + 1 = a² - 6a² + 5a² + 1 = 6a² - 6a² + 1 = 1  

а=-в

(-в)²+6(-в)*в+5в²+1=в²-6в²+5в²+1=1