# How do you factor completely #21x^2 + 27x - 30#?

##### 1 Answer

May 1, 2016

#### Answer:

Always look for a common factor in all the terms first.

#### Explanation:

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