Answer:
(x - 3)(x - 7)
Explanation:
Please use the symbol " ^ " for exponentiation: x^2 - 10x + 21.
Note that 3*7 = 21 and that 3+7 = 10. These are the clues we need to factor x^2 - 10x + 21. If we factor by grouping, we get:
x^2 - 10x + 21 = (x - 3)(x - 7). Note how -3x and -7x add up to -10 x (as they should), and that -3 times -7 is +21 (as required).