Question

How can i solve by completing the square 4r^2-28r=-49

Answer 1

To complete the square, the second degree term must have a coefficient of 1.
Since the second degree term here has a coefficient of 4, we start by dividing each term on both sides by 4.

$4r^2 - 28r = -49$

$\dfrac{4r^2}{4} - \dfrac{28}{4}r = -\dfrac{49}{4}$

$r^2 - 7r = -\dfrac{49}{4}$

Now we can complete the square.
First, we need to find what number completes the square.
We take the coefficient of the first degree term, -7 in this case.
Divide it by 2 and square it. -7 divided by 2 is the fraction -7/2.
Now we square -7/2 to get 49/4.
We add 49/4 to both sides.

$r^2 - 7r + \dfrac{49}{4} = -\dfrac{49}{4} + \dfrac{49}{4}$

$(r - \dfrac{7}{2})^2 = 0$

$r - \dfrac{7}{2} = 0$

$r = \dfrac{7}{2}$