a-maths!!!!

設P點為( b2 / 4, b ), M點為( x, y )。
根據已知條件:
x = [ ( 2 )( 4 ) + ( 1 )( b2 / 4 ) ] / ( 1 + 2 )
x = ( 8 + b2 / 4 ) / 3 --- ( 1 )
y = [ ( 2 )( 6 ) + ( 1 )( b ) ] / ( 1 + 2 )
3y = 12 + b
b = 3y – 12 --- ( 2 )
代( 2 )入( 1 ),
x = [ 8 + ( 3y – 12 )2 / 4 ] / 3
3x = 8 + ( 3y – 12 )2 / 4
12x = 32 + 9y2 – 72y + 144
所以9y2 – 12x – 72y + 176 = 0 是M點的軌距方程。