text: a-level mathematics problem!!? prove that (24-x)(x-8)-k is negative for all real values of x provided that k>64 hence show that expression (6+y)(4-y)(y+4)(y-2)-65 is negative for all real values of y use the formula b*2-4ac<0 because for if all values of x is negative then the curve will pass totally under the x-axis  b*2 is b to the power of 2