How do you solve the quadratic X^2 - 8X + 15 = 0 ?

First factorise (using a "farmer's field", will draw this on whiteboard):=> (X-3)(X-5) = 0Hence using the zero rule (one of the brackets must be equal to 0 if the product is 0),either X-3 = 0 OR X-5=0=> X=3 or X=5Check by substituting back into the original equation:(3)^2 - 8(3) + 15 = 09 - 24 + 15 = 0-15 + 15 = 0 (correct)and(5)^2 - 8(5) +15 = 025 - 40 +15 = 0-15 + 15 = 0 (correct).