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What are the soultion(s) to the quadratic equation 40- x^2=0

The number if marbles of different colors stored in a hat is listed below: 4 red marbles 10 green marbles 7 blue marbles. without looking in the hat, dan takes out a marble at random. he replaces the marble and then takes out another marble from the hat. what is the probability that dan takes out a blue marble in both draws?

If cos(2x) = tan^2(y), show that cos(2y) = tan^2(x).