Question 1164844
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Your equation is

    x*(3x-4) = 20,


as the other tutor explained you.


I will show you a trick allowing solve it mentally.


Multiply both sides by 3 (the same coefficient, which is at  "3x").  You will get

    3x*(3x-4) = 3*20 = 60.


So, 60 is presented as the product of two numbers (factors) that differ by 4.


Now think, which two integers that differ by 4 give 60 as the product.


But of course, they are 6 and 10  (or -6 and -10).


In the first case, you have 3x = 10, which does not produce integer x.


In the second case,  3x = -6,  giving an integer solution x = -2,  which is your answer.
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Solved &nbsp;&nbsp;&nbsp;&nbsp;// mentally.