(5x-1)(5x+1)+(5x+1)=25x²-1+5x+1=25x²+5x.

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(a-b)(a+b)=a²-b².

Ответ:

(5х-1)(5х+1)+(5х+1)=((5х)^2-1^2)+(5х+1)=

=25х^2-1+5х+1=25х^2+5х