factor completely please?

49s^2 -42s + 9 ---> given

(7s - 3) (7s - 3 ) ---> final answer

by checking:
we have -3 x 7s = 21s
-3 x 7s = 21 s
combining we have -42s

7s X 7s = 49s^2

and -3 x -3 = 9

therefore we have again:
(7s - 3) (7s - 3 ) ---> final answer

49s^2 + 9 - 42s =

Rearrange.
49s^2 - 42s + 9 =

Notice that the first and last terms are perfect squares.
49s^2 = 7s * 7s = (7s)^2
9 = 3 * 3 = (3)^3

Don't forget the negative factors.
49s^2 = -7s * -7s = (-7s)^2
9 = -3 * -3 = (-3)^3

49s^2 - 42s + 9 =
(7s)^2 - 42s + (3)^2 =

We know that:
(a + b)^2 = a^2 + 2ab + b^2

Check to see if the middle term -42s fits this pattern.
-42s = 2 * 7s * 3?
-42s = 42s?
FALSE

Don't forget to check the other possible pairs.
-42s = 2 * 7s * -3?
-42s = -42s
TRUE

(a + b)^2 = a^2 + 2ab + b^2
(7s - 3)^2 = (7s)^2 + 2(7s)(-3) + (-3)^2
(7s - 3)^2 = 49s^2 - 42s + 9

ANSWER: (7s - 3)^2 = 49s^2 - 42s + 9

49s^2 + 9 - 42s
= 49s^2 - 42s + 9
= 49s^2 - 21s - 21s + 9
= (49s^2 - 21s) - (21s - 9)
= 7s(7s - 3) - 3(7s - 3)
= (7s - 3)(7s - 3)
= (7s - 3)^2

49 s ² - 42 s + 9

(7 s - 3 ) (7 s - 3)

( 7 s - 3 ) ²