Maths

Method 1:
7n² + 9n - 500 > 0
7n² + 9n > 500
7[n² + (9/7)] > 500
7[n² + (9/7) + (9/14)²] > 500 + 7*(9/14)²
7[n + (9/14)]² > 14081/28
n + (9/14) > (√14081)/14 or n + (9/14) <-(√14081)/14
n > (-9 + √14081)/14 or n < (-9 - √14081)/14


Method 2:
7n² + 9n - 500 > 0
7 [n - (-9 + √14081)/14] [n - (-9 - √14081)/14] > 0
n > (-9 + √14081)/14 or n < (-9 - √14081)/14

micatkie個答案有問題 5係乘負數只係加減5洗轉符號
n > (-9 + √14081)/14 or n > (-9 - √14081)/14
之後
n > (-9 + √14081)/14 > (-9 - √14081)/14
所以
n > (-9 + √14081)/14 咁先岩