General simplification
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$$- y^{2} - 9 y - 4$$
/ ____\ / ____\
| 9 \/ 65 | | 9 \/ 65 |
|x + - + ------|*|x + - - ------|
\ 2 2 / \ 2 2 /
$$\left(x + \left(\frac{9}{2} - \frac{\sqrt{65}}{2}\right)\right) \left(x + \left(\frac{\sqrt{65}}{2} + \frac{9}{2}\right)\right)$$
(x + 9/2 + sqrt(65)/2)*(x + 9/2 - sqrt(65)/2)
The perfect square
Let's highlight the perfect square of the square three-member
$$\left(- y^{2} - 9 y\right) - 4$$
To do this, let's use the formula
$$a y^{2} + b y + c = a \left(m + y\right)^{2} + n$$
where
$$m = \frac{b}{2 a}$$
$$n = \frac{4 a c - b^{2}}{4 a}$$
In this case
$$a = -1$$
$$b = -9$$
$$c = -4$$
Then
$$m = \frac{9}{2}$$
$$n = \frac{65}{4}$$
So,
$$\frac{65}{4} - \left(y + \frac{9}{2}\right)^{2}$$
Assemble expression
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$$- y^{2} - 9 y - 4$$
Rational denominator
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$$- y^{2} - 9 y - 4$$
Combining rational expressions
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$$y \left(- y - 9\right) - 4$$