Find the interval for which x^2 - 7x + 10 </= 0

Factorise the quadratic by finding two numbers that add to make -7 and multiply to make 10. (i.e. -2 and -5). So x^2  -  7x +  10 = (x - 2)(x - 5) </= 0. Sketch the quadratic to see where it is negative or zero. Find that the interval is 2 </= x </= 5.