Question 337931
-2t^2+5t-15=0 This is correct. Well done!
This is a quadratic equation. The quadratic equation gives no real numbers as answers. 
If you are familiar with imaginary numbers the answer is:
t=5/4 + sqrt(95)/4 * i,  t=5/4 - sqrt(95)/4 * i (See below)
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Ed
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 *[invoke quadratic "x", -2, 5, -15]