Thực hiện mỗi phép tính sau: a) x^2 + 1/4 x^2 - 5x^2; b) y^4 + 6y^4 -2/5 y^4;

a) x² + $\frac{1}{4}$x² - 5x² = $\left(1+\frac{1}{4}-5\right)$x² = $\left(\frac{4}{4}+\frac{1}{4}-\frac{20}{4}\right)$x² = $\frac{-15}{4}$x².

b) y⁴ + 6y⁴ - $\frac{2}{5}$y⁴ = $\left(1+6-\frac{2}{5}\right)$y⁴ = $\left(\frac{5}{5}+\frac{30}{5}-\frac{2}{5}\right)$y⁴ = y⁴.