21000=20000(1+0,02)^t
-(ln(x))/x - (1/x) =
(1/4) ^-3
x^4-18x^2+81
−108π=6πj
$7^{2x+3}$+42* $7^{x}$-1=0
f=-4.9x^2+20x
b=x1/4 × x3/4
-4x-6=-2x-4