How di I turn a decimal like -4.646 into a number like -2 - sqrt(7)
-2 - √ 7 is an irrational number [ can't be expressed as a fraction]
But -4.646 is rational [ can be expressed as a fraction ]
So......it's impossible to turn a rational into an irrational - and vice-versa......
Were you trying to solve an equation,OBT????
If so...post the problem and we'll see if we can solve it