Answer
$z=1.68,8.32$
Work Step by Step
$4p^2-40p+56=0$
or, $4p^2-40p=-56$
or, $p^2-10p=-14$
Compare it with the standard form of quadratic equation $ax^2+bx+c$, we have $a=1, b=-10$
Therefore, $b^2=4ac$ $\implies$ $c=\dfrac{b^2}{4a}$
Thus, $c=\dfrac{b^2}{4a}=\dfrac{(-10)^2}{4}=25$
To complete the square, add $\dfrac{49}{4}$ on both sides.
$p^2-10p+25=-14+25$
$\implies (p-5)^2=11$
$\implies (p-5)=3.32$
and
$\implies (p-5)=-3.32$
or, $z=1.68,8.32$
