Answer
$\dfrac{7}{15}x^{4}-18x^{2}-5$
Work Step by Step
$\dfrac{2}{5}x^{4}-23x^{2}+\dfrac{1}{15}x^{4}+5x^{2}-5$
Simplify by combining like terms:
$\Big(\dfrac{2}{5}+\dfrac{1}{15}\Big)x^{4}+(5-23)x^{2}-5=\Big(\dfrac{30+5}{75}\Big)x^{4}-18x^{2}-5=...$
$...=\dfrac{35}{75}x^{4}-18x^{2}-5=\dfrac{7}{15}x^{4}-18x^{2}-5$