f2. 好難呀help!!

Let the intersecting point of the red dots and blue dots be the origin, so the 2 black dots are (-1, 10) and (5,8).
Let the blue dot be (b,0),
so (b + 1)^2 + 10^2 = (b - 5)^2 + 8^2
b^2 + 1 + 2b + 100 = b^2 - 10b + 25 + 64
2b + 101 = - 10b + 89
12b = - 12
b = -1 which is the 5th dot from left.
Let the red dot be (0,r)
so 1^2 + ( 10 - r)^2 = 5^2 + ( 8 - r)^2
1 + 100 + r^2 - 20r = 25 + 64 + r^2 - 16r
101 - 20r = 89 - 16r
12 = 4r
r = 3 which is the 9th red dot from above.

藍點由左至右第5個 ; 距離=√(6^2+8^2) = 10
紅點由上至下第9個 ; 距離=√(1^2+7^2) = √(5^2+5^2)
1米等於100厘米
1立方米等於100*100*100 = 1,000,000立方厘米