solve x2+10x+21=0 ...?
x²+10x+21=0/\ = 10²-4121/\ = 100 - 84/\ = 16x = (-10+/-\/16)/2x = (-10+/-4)/2x' = (-10+4)/2 = -6/2 = -3x" = (-10-4)/2 = -14/2 = -7S: {-3; -7}
