Question

Solve for x.

Use the completing the square method.


4x2−7x−8=0


Round decimals to the nearest tenth.

Answer 1

x = 2.5 or -0.8

Explanation:

Here, we are to use completing the square method to solve for the values of x

Firstly, we divide through by 4

= x^2 -7/4x -2 = 0

Now, we move the two term to the right hand side

x^2 -7/4x = 2

Now, we divide the coefficient of x by 2 and square it;

That would be;

(-7/4 * 1/2)^2 = 49/64

we now add this value to both sides of the equation

x^2 -7/4x + 49/64 = 2 + 49/64

The right hand side can be rewritten as;

(x-7/8)^2 = 177/64

taking the square root of both sides

x-7/8 = √(177/64)

x = 7/8 ± √(177/64)

x = 7/8 + √(177/74) or 7/8 - √(177/64)

= x = 2.53802 or -0.788017

Which to the nearest tenth is

x = 2.5 or -0.8