a) (x√2 + 1)² - (x√2 -1)² = √2
formula: a² - b² = (a+b)(a-b)
2x√2 ·2 = √2 4x = 1 X = 1/4
b) x² + 6x +8 - x² +1 = x - 1
5x = - 10 x = - 2
c) [1/(x-1)]^-1 + [1/(x-2)]^-1 + ............+ [1/(x-100)]^-1 = 0
x - 1 + x-2 +x-3+..............+x-100 = 0
100x - (1+2+3+...........+100) = 0
100x = 100·101/2 x = 101/2