20d^2-17dr-63r^2. Note: changed your variables d, r into x, y. Just substitute.
Factor the following:
20 x^2-17 x y-63 y^2
The coefficient of x^2 is 20 and the coefficient of y^2 is -63. The product of 20 and -63 is -1260. The factors of -1260 which sum to -17 are 28 and -45. So 20 x^2-17 x y-63 y^2 = 20 x^2-45 x y+28 x y-63 y^2 = 4 x (5 x+7 y)-9 y (5 x+7 y):
4 x (5 x+7 y)-9 y (5 x+7 y)
Factor 5 x+7 y from 4 x (5 x+7 y)-9 y (5 x+7 y):
Answer: |
| (5x + 7y) (4x - 9y)
