Answer:
9d² - 49
Explanation:
(3d + 7)(3d - 7) =
= 3d × 3d + 3d × (-7) + 7 × 3d + 7 × (-7)
= 9d² - 21d + 21d - 49
= 9d² - 49
That is the solution obtained by multiplying the first binomial by the second binomial term by term.
If you are familiar with the product of a sum and a difference which equals a difference of squares, whose pattern is: (a + b)(a - b) = a² - b², then you can immediately get the answer in one step.
(3d + 7)(3d - 7) =
= 9d² - 49