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For what value of c does the quadratic function f(x)=x^2-6x+c have exactly one x-intercept? For what value of c does the quadratic function f(x)=x^2-6x+c have directly one x-intercept? Which of the two sciences is the best, physics or stamp collecting ? What is the source of vitamin c in supplements? I know some of it comes from plants but how do companies get it? (is any of it from grapes?)? What is 2/3 of 7.0?