Maths 坐標

2014-11-29 1:38 am

設x坐標為 (3,5)求 x 轉動以下角度後的坐標
A. 順時針90°
B.順時針180°
C. 順時針270°

回答 (4)

2014-11-29 3:33 am
✔ 最佳答案
其實你地使乜講到咁啫!
畫graph就得架喇!(沿住點O)
或者你可以咁諗:
用x點同x-axis整個直角三角形出嚟
x順時針轉咗90度就等於將佢長度放喺y-axis上面
如此類推
A:(5,-3)
B:(-3,-5)
C:(-5,3)
2014-11-29 4:31 am
考慮風車畫法:

    (-2,4)
      XX
      XX
      XXOOOO(4,2)
      XXOOOO
    AAAABB
    AAAABB
(-4,-2) BB
        BB(2,-4)

   (x,y)
順=>(y,-x)
順=>(-x,-y)
順=>(-y,x)

2014-11-28 20:33:12 補充:
(a,b) 順時針90度得 (b,-a)

(a,b) 逆時針90度得 (-b,a)
2014-11-29 2:39 am
The Cartesian Coordinates (x,y) can be firstly converted into Polar Coordinates (r,θ):
r = √ ( x^2 + y^2 )= √ ( 3^2 + 5^2 )= √34
θ = tan-1 ( y / x )= tan-1 ( 5 / 3 )=59.036…°
After rotation, the Polar Coordinates (r,θ) are converted back to Cartesian Coordinates (x,y).

a. Clockwise 90°, i.e. θ becomesθ-90°=θ- (360°-270°) = -360°+(θ+270°)=θ+270°
Convert the rotated Polar Coordinates (r,θ) to Cartesian Coordinates (x,y) :
x = r × cos( θ+270°)= √34×cos(59.036°+270°)=5
y = r × sin( θ+270°) = √34×sin(59.036°+270°)=-3

b. Clockwise 180°, i.e. θ becomes θ-180°=θ- (360°-180°) = -360°+(θ+180°)=θ+180°
Convert the rotated Polar Coordinates (r,θ) to Cartesian Coordinates (x,y) :
x = r × cos( θ+180°)= √34×cos(59.036°+180°)=-3
y = r × sin( θ+180°) = √34×sin(59.036°+180°)=-5

c. Clockwise 270°, i.e. θ becomes θ-270°=θ- (360°-90°) = -360°+(θ+90°)=θ+90°
Convert the rotated Polar Coordinates (r,θ) to Cartesian Coordinates (x,y) :
x = r × cos( θ+90°)= √34×cos(59.036°+90°)=-5
y = r × sin( θ+90°) = √34×sin(59.036°+90°)=3
2014-11-29 1:46 am
Maths 坐標

B.順時針180°


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