$sin\left(\frac{4\pi}{7}\right)cos\left(\frac{5\pi}{21}\right)-cos\left(\frac{4\pi}{7}\right)sin\left(\frac{5\pi}{21}\right)$

$-6x^2-1\ge0$

$\int\frac{2}{5}e^{7x-1}dx$

$28a^5+14a^4-7a^7$

$n=\frac{\left(5x+1\right)^2+5\left(x-1\right)^2}{5x^2+1}$

$-2x^6+26x^7-18x^8-120x+120=6x^7$

$\frac{1080}{10}$