Let f(x)=(x-1)(x+2)(2x-5)f(x)=(x−1)(x+2)(2x−5)
Now, we can do our sign chart
color(white)(aaaa)aaaaxxcolor(white)(aaaaaa)aaaaaa-oo−∞color(white)(aaa)aaa-2−2color(white)(aaaa)aaaa11color(white)(aaaa)aaaa5/252color(white)(aaaaa)aaaaa+oo+∞
color(white)(aaaa)aaaax+2x+2color(white)(aaaaaa)aaaaaa-−color(white)(aaaa)aaaa++color(white)(aaa)aaa++color(white)(aaaa)aaaa++
color(white)(aaaa)aaaax-1x−1color(white)(aaaaaa)aaaaaa-−color(white)(aaaa)aaaa-−color(white)(aaa)aaa++color(white)(aaaa)aaaa++
color(white)(aaaa)aaaa2x-52x−5color(white)(aaaaa)aaaaa-−color(white)(aaaa)aaaa-−color(white)(aaa)aaa-−color(white)(aaaa)aaaa++
color(white)(aaaa)aaaaf(x)f(x)color(white)(aaaaaaa)aaaaaaa-−color(white)(aaaa)aaaa++color(white)(aaa)aaa-−color(white)(aaaa)aaaa++
Therefore,
f(x)<0f(x)<0 when x in ] -oo,-2 [ uu ] 1, 5/2[ x∈]−∞,−2[∪]1,52[