Question

розвяжить неривнисть -x²+2x+15>0

Answer 1

$-x^2+2x+15>0\\-x^2+5x-3x+15>0\\-x(x-5)-3(x-5)>0\\-(x-5)(x+3)>0\\(x-5)(x+3)<0\\\left \{ {{5-x<0} \atop {x+3>0}} \right. \to \left \{ {{5-x>0} \atop {x+3<0}} \right. \\x \in (-3;5)$