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1. a+b+c=30

2. a+b=30-c

3. squaring on both sides a²+2ab+b²=900-60c+c²

4. by pythagoras theorem- a²+b²+c²

5. so 2ab=900-60c

6. Dividing by two ab=450-30c

7. so the area of the triangle= ab/2 (450-30c)/2

8. so the area of the triangle is 225-15c