I need help with this maths question: Solve by completing the square and write your answers correct to 3 significant figures y^2 - 40y - 3 = 0

2 Answers

lemjay's profile pic

lemjay | High School Teacher | (Level 3) Senior Educator

Posted on


To solve using the completing the square method, isolate the constant.



Then, determine the number that should be added on both sides of the equation. To do so, take half of coefficient of y. And square it.





Then, factor left side.


And, isolate y.




`y=+-sqrt403 + 20`

The `+-` signs before the square root indicates that there are two values of y which are:



Since the values should be express with three significant figure,  then, the solutions to the given equation are y={-0.075, 40.1}.

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oldnick | (Level 1) Valedictorian

Posted on


let we solve it:

`y^2 -(2)(20)+400-403=0 `