Hello! So, this question is in the form of ax² - bx - c. First thingd first, let's multiply a and c together. c = -8 and a = 5. -8 * 5 is -40. Now, let's find two factors that have a product of 40, but a sum of 18. If you list the factors, you see that 2 and 20 have a product of 40, but 2 - 20 is -18. The factors we will use are -2 and 20.
How to factor it:
For this question, you can use something called a box method and factor it by finding a factor of each column and row. Just make 4 boxes and put 5x² on the top left and -40 on the bottom left box. Put 2x on the top right box and -20x on the bottom left box. Now, factor out for each row and column. The factors should be 5x + 2 for the top part and x - 4 for the side. It should look like (5x + 2)(x - 4). Let's check it. Solve it by using the FOIL method and you get 5x² - 20x + 2x - 8. Combine like terms and you get 5x² - 18x - 8. There. The answer is B: (5x + 2)(x - 4)
Note: The box method may be challenging at first, but it can be really helpful on problems like these.
First you have to square the radius. So for this question you multiply 5x5. That makes 25. Then you multiply that with pi ( 3.14 ) and that makes 78.50. Next you multiply it by 9, that makes 706.5.