First find the law, and then calculate "5 + 10 + 15 + 20 +... + 300 =? Please advise

First find the law, and then calculate "5 + 10 + 15 + 20 +... + 300 =? Please advise

"5 + 10 + 15 + 20 +... + 300" has 600 numbers
Let a = 5 + 10 + 15 + 20 +... + 300
A=300+295+290+285+...+5
2A=305*600
A=305*300=91500

Given the quadratic function y = ax ^ 2 + BX + C, A0, C > 0, the symmetry axis of the function is x = 1, and the vertex is in the first quadrant

2C0, i.e
Y = - X & sup2; + 2x + C = - (x-1) & sup2; + (c + 1) the vertex is (1, C + 1)
Satisfy the given conditions of A0, C > 0, the axis of symmetry of the function is x = 1, and the vertex is in the first quadrant
Then:
When C > 3, 2C > 6 = 3B
When C = 3, 2C = 6 = 3B
When 0