tan -2800degrees
f(x) = -2x(x-1)(x+2)
$$6x=\frac{x}{30}$$
f(x) = 3x^2 - 7x
tan 780degrees
5^2+2^2=x^2 then x=?
f(x) = (x+1)(x^2-10x+21)
f(x) = 3x^3 - 10x^2 +7x
$$\sum_{n=1}^{ \infty}{\frac{1}{n^2(8n+1)^2}}$$
25^x-4,5^x=25