Question 985865
Expand using distribution. Start by expanding the first two terms. Then do that again using the result of the first expansion and the remaining term. As follows

{{{(1-a)(1-b)(1-c)}}}
{{{(1(1-b) -a(1-b)) * (1-c)}}}
{{{(1-b -a+ab) (1-c)}}}
{{{1 -c -b +bc -a +ac +ab -abc}}}
{{{1 -a - b -c +ab + ac + bc - abc}}}