1.Problem 3. 5 x 2 + 18 x + 9. Show Factors By Grouping. Use the formula. Product of (a)(c) = (5)(9) = 45. ... 2)Problem 4. 2x² + 5x + 3. Factor it. Apply our formula. ... 3)Problem 5. 5x² + 13x + 6. Factor By Grouping. Remember our formula. ... 4)Problem 6. 7x² + 9x + 2. Factor By Grouping. You know the deal-- Use our formula for factoring by grouping. there are some EX's