Rewrite e2t as (et)2.
Let u=et. Substitute u for all occurrences of et.
Factor using the perfect square rule.
Rewrite 1 as 12.
Check that the middle term is two times the product of the numbers being squared in the first term and third term.
Rewrite the polynomial.
Factor using the perfect square trinomial rule a2+2ab+b2=(a+b)2, where a=u and b=1.
Replace all occurrences of u with et.