The missing factor is (a -1) I believe. If you foil (5a + 9)(a - 1) you would get 5a^2 + 4a - 9.
B. (k+10f)(k-5f) you can tell in 2 ways. 1. if the second sign is neg then the signs in the factors are going to be one neg and one positive so that knocks out C and D. Then you look at the second term and since the 5 is positive then the 10 has to be positive so you end up with a positive 5kf.
The second way is to FOIL them out. When you check B you get

combine your like terms and you have your original expression of

Hope that helps
Answer:
is it an abc or what??
Step-by-step explanation:
Step-by-step explanation:
=11/3×1/14
=3.67×0.07
=0.2568
Answer:
0.5 ≥ x ≥ 0.35
Step-by-step explanation: