Question 215011
How to solve 42 = -21t + 4.9t^2


Step 1.  Subtract 42 from both sides of the equation and rearrange right side


{{{42-42 = -21t + 4.9t^2-42}}}


{{{0= 4.9t^2-21t-42}}}


{{{4.9t^2-21t-42=0}}}


Step 2.  We can use the quadratic formula given as 


{{{x = (-b +- sqrt( b^2-4*a*c ))/(2*a) }}}


where a =4.9, b=-21, and c=-42


*[invoke quadratic "t", 4.9, -21, -42 ]


I hope the above steps were helpful.


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Good luck in your studies!


Respectfully,
Dr J