Question 541506
Here is a general case of the squaring:
{{{ (a - b)2 = (a - b)*(a - b) }}}
{{{ (a - b)*(a - b) = a^2 - a*b - a*b + b^2 }}}
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Now your problem:
{{{ (5x - 1)^2 = (5x - 1)*(5x - 1) }}}
{{{ (5x - 1)*(5x - 1) = 25x^2 - 5x - 5x + 1 }}}
{{{ (5x - 1)*(5x - 1) = 25x^2 - 10x + 1 }}} 
In the FOIL method, the {{{ -5x }}} terms come
from the Outer and Inner multiplications.