Problem Solving (PS) | Re: If (x - 1)^2 = 400 which of the following could be the value

(x-1)^2= 400
(x-1)^2= (20)^2

(x-1)^2 -(20)^2= 0

Use identity a^2-b^2= (a+b)*(a-b)

(x-1+20)(x-1-20)=0
(x+19) (x-21)=0

Equate the factorized form to zero.

x= -19 or x= 21

Plug in (x-5) and check the options.


If I took (-20)^2

(x-1)^2 - (-20)^2= 0

(x-1-20)* (x-1+20)= 0

(x-21) (x+19)= 0

x= 21 or x= -19


Same answer.

This identity: a^2-b^2= (a+b)(a-b) comes in handy in many questions.

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