Find a formula for p(x) = P(X=x)

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To find the formula for p(x) = P(X=x) where X is a random variable taking values a and b, the probabilities are defined as P(X=a)=p and P(X=b)=1-p. The expected value E(X) can be expressed as E(X) = a*p + b*(1-p). This shows that the expected value is a weighted average of the two possible values, a and b, based on their probabilities. Understanding the relationship between mu and the probabilities is essential for solving related problems in probability theory. The discussion emphasizes the importance of correctly applying these concepts in preparation for the test.
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Find a formula for p(x) = P(X=x) ...

So I have a test tomorrow and this question is in a list of review questions and I'm having trouble remembering where the mu fits into the formula. Any help would be greatly appreciated :)

Question: Suppose that X is a random variable with just two possible values a and b. For x = a and b find a formula for p(x) = P(X = x) in terms of a, b and mu = E(X).
 
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If P(X=a)=p and P(X=b)=1-p, what can you say about E(X)?
 

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