Question

Explain why please and make sure it is in full detail

Answer 1

Step-by-step explanation:

well,

(y - 7)² = (y - 7)(y - 7)

remember how to multiply 2 expressions ?

you have to multiply every term of one expression with every term of the other expression and sum the results all up (incl. considering their individual signs, of course).

so, when we do the multiplication, we get

(y - 7)(y - 7) = y×y - 7×y - 7×y + (-7)×(-7) =

= y² - 14y + 49

and that is clearly different to y² - 49

FYI

y² - 49 is the result of

(y - 7)(y + 7)

because

y×y + 7×y - 7×y + (-7)(7) = y² - 49

Answer 2

Answer:

The exponent of an expression says how many times to multiply the expression.

$\implies (y-7)^2=(y-7)(y-7)$

Expand the brackets:

$=y^2-7y-7y+49$

Combine like terms:

$=y^2-14y+49$

- - - - - - - - - - - - - - - - - - - - - - -

$y^2-49=(y+7)(y-7)$

Using "Difference of Two Squares" $a^2-b^2=(a+b)(a-b)$