1.a = n + b a^2 + 2b^2 = 15(n+b)^2 + 2b^2 = 15n^2 + 2nb + 3b^2 = 15 n = 0, 1, 2或 3 n = 39 + 6b + 3b^2 = 15b^2 + 2b – 2 = 0b = √3 – 1, -√3 – 1 (不合)a + 2b = (3 + √3 – 1)+ 2(√3 – 1) = 1 + 2√3 = 3√3 n = 24 + 4b + 3b^2 = 153b^2 + 4b – 11 = 0b = (-2 ±√37)/3 (不合)同理, n = 0, 1, b > 1, 不合 所以a + 2b = 3√3 2.a^2 + b^2 = 18n^2 + 2nb + 2b^2 = 18n = 0, 1, 2, 3, 4 n = 416 + 8b + 2b^2 = 18b^2 + 4b – 1 = 0b = √5 – 2, -√5 – 2(不合)n = 0, 1, 2, 3, b > 1 所以 a + b = (4 + √5 – 2) + (√5 – 2) = 2√5 3.5|a-1|+2|b+1|+|c-2|= 4 a – 1 = 0, a = 1 (|b+1|,|c-2|)= (2,0),(1,2),(0,4) (b + 1 , c – 2) =( ±2,0) ,( ± 1, ±2),(0, ± 4)(b,c) = (-1 ±2,2+0), ( -1± 1,2 ±2), (-1+0,-2 ± 4) (a,b,c) = (-1,1,2),(-1,-3,2), (-1,0,4),(-1,-2,4),(-1,0,0),(-1,-2,0), (-1,-1,2),(-1,-1,-6) 八個