1) Probe whether this is a perfect square trinomial, i.e a trinomial that can be factored as (a + b)^2 or (a - b)^2.:
2) Determine if the first and the third terms of the trinomial (once it is ordered, which it is) have exact square roots:
√ (d^2) = d
√49 = 7
3) Since they have exact square roots, test wether the second term of the trinomial equals twice the product of the two square roots determined:
=> 2 * (d) * (7) = 14d which is exactly the second term of the trinomial
4) Now you can write the binomial squared using the sign of the second term. This is:
(d - 7)^2.
You can prove that that is the answer by expanding the binomial squared, which must drive back to the original expression: d^2 - 2(7)(d) + 7^2 = d^2 - 14d + 49.
