How do you factor completely #21x^2 + 27x - 30#?
Always look for a common factor in all the terms first.
3 is a factor of 21, 27 and 30. Taking it out gives
The quadratic trinomial inside the bracket seems not to factorise further, because there are no factor combinations of 7 and 10 which subtract to give 9. The only possibilities are 4, 9, 33 and 69. However, another approach would be to find the factors of 70, (
Using the method of grouping gives the following:
The final answer would be