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Factor ( ² - 81).

a. ( r -9 ) ( r -9 )
b. ( r - 9) ( r + 9)
c. ( r + 9 ) ( r + 9)​


Sagot :

Answer:

b. (r-9) (r+9)

Step-by-step explanation:

In (r-9) (r+9) using foil method

F = r²

O = +9r

I = -9r

L = -81

so:

r²-81

Explaination:

r times r is equal to r²

r times positive 9 is equal to +9r

r times negative 9 is equal to -9r

+9 multiply by -9 is equal to -9 (negative by negative = positive, positive by negative = negative, negative by negative = positive)

+9r and -9r will cancel each other so 0.