Question 386461
There's not a closed form solution.
You need to use Newton's method.
You're solving for the intersection of a line with the exponential curve.
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{{{graph(300,300,-10,10,-10,10,0,e^(x),x-1,x+1,x+3)}}}
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As you see, you can have 0, 1, or 2 solutions depending on {{{a}}}.