Question 1135371
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Your post should contain a question.  Although it is obvious what your question probably is, it would be more polite if you asked it, instead of making us guess.<br>
(1) {{{a+ar+ar^2 = 42}}}
(2) {{{ar^3-a = 42}}}<br>
{{{ar^3-a = a(r^3-1) = a(r-1)(r^2+r+1) = 42(r-1) = 42}}}
{{{r-1 = 42/42 = 1}}}
{{{r = 2}}}<br>
Substituting in (2),<br>
{{{a(8)-a = 42}}}
{{{7a = 42}}}
{{{a = 6}}}<br>
The GP is 6, 12, 24, 48, ...