The perfect square
Let's highlight the perfect square of the square three-member
$$\left(y^{4} - y^{2}\right) - 6$$
To do this, let's use the formula
$$a y^{4} + b y^{2} + c = a \left(m + y^{2}\right)^{2} + n$$
where
$$m = \frac{b}{2 a}$$
$$n = \frac{4 a c - b^{2}}{4 a}$$
In this case
$$a = 1$$
$$b = -1$$
$$c = -6$$
Then
$$m = - \frac{1}{2}$$
$$n = - \frac{25}{4}$$
So,
$$\left(y^{2} - \frac{1}{2}\right)^{2} - \frac{25}{4}$$
General simplification
[src]
$$y^{4} - y^{2} - 6$$
/ ___\ / ___\ / ___\ / ___\
\x + \/ 3 /*\x - \/ 3 /*\x + I*\/ 2 /*\x - I*\/ 2 /
$$\left(x - \sqrt{3}\right) \left(x + \sqrt{3}\right) \left(x + \sqrt{2} i\right) \left(x - \sqrt{2} i\right)$$
(((x + sqrt(3))*(x - sqrt(3)))*(x + i*sqrt(2)))*(x - i*sqrt(2))
Assemble expression
[src]
$$y^{4} - y^{2} - 6$$
Rational denominator
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$$y^{4} - y^{2} - 6$$
/ 2\ / 2\
\-3 + y /*\2 + y /
$$\left(y^{2} - 3\right) \left(y^{2} + 2\right)$$
Combining rational expressions
[src]
$$y^{2} \left(y^{2} - 1\right) - 6$$