x2 - 5x + 4 = 0

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Assuming you mean x^2-5x+4=0, you can factor it to:(x-4)(x-1) = 0.The solutions are x=4 and x=1.

As an alternative, you can use the quadratic formula.x^2 - 5x + 4ax^2 + bx + cx = (-b ± √(b^2 -4ac))/2ax = (5 ± √(25 - 16))/2x = 4, 1There are two reasons I prefer this option.  First, I'm terrible at factoring so this offers an easy alternative, and second, sometimes factoring isn't an option to begin with.