Answer: (3b + 5)(3b - 5)
Because both terms, 9b² and 25, are perfect squares, you can factor by taking the square roots of both terms.
The square root of 9b² is 3b (3b × 3b = 9b²).
The square root of 25 is 5 (5 × 5 = 25).
9b² - 25 has a negative, so the factored expression would be
(3b + 5)(3b - 5). The signs (+ and -) alternate in this case because the expression, 9b² - 25, has no middle term.
You can check your work by using FOIL. See the attachment below.
F irst
O utside
I nside
L ast
