由于2到1和1到3的向量垂直,它们的点积为0。
这让你有两个未知数:从1到3的x(x13)和从1到3的y(y13)
使用勾股定理得到这些未知数的另一个方程。
通过代换解决每个未知数...
这需要平方和开方,因此您会失去与方程相关联的符号。
要确定符号,请考虑:
while x21 is negative, y13 will be positive
while x21 is positive, y13 will be negative
while y21 is positive, x13 will be positive
while y21 is negative, x13 will be negative
已知:点1坐标为x1,y1
已知:点2坐标为x2,y2
x21 = x1 - x2
y21 = y1 - y2
已知:距离 |1->3| : N/2
方程 a: 勾股定理
x13^2 + y13^2 = |1->3|^2
x13^2 + y13^2 = (N/2)^2
已知:角2-1-3为直角
向量2->1和1->3互相垂直
2->1点乘1->3等于0
方程b:点积等于0
x21*x13 + y21*y13 = 2->1 dot 1->3
x21*x13 + y21*y13 = 0
x13和y13之间的比率:
x21*x13 = -y21*y13
x13 = -(y21/x21)y13
x13 = -phi*y13
方程a:已知比例求解y13
plug x13 into a
phi^2*y13^2 + y13^2 = |1->3|^2
factor out y13
y13^2 * (phi^2 + 1) =
plug in phi
y13^2 * (y21^2/x21^2 + 1) =
multiply both sides by x21^2
y13^2 * (y21^2 + x21^2) = |1->3|^2 * x21^2
plug in Pythagorean theorem of 2->1
y13^2 * |2->1|^2 = |1->3|^2 * x21^2
take square root of both sides
y13 * |2->1| = |1->3| * x21
divide both sides by the length of 1->2
y13 = (|1->3|/|2->1|) *x21
lets call the ratio of 1->3 to 2->1 lengths psi
y13 = psi * x21
check the signs
when x21 is negative, y13 will be positive
when x21 is positive, y13 will be negative
y13 = -psi * x21
方程a:以比例解决x13问题
plug y13 into a
x13^2 + x13^2/phi^2 = |1->3|^2
factor out x13
x13^2 * (1 + 1/phi^2) =
plug in phi
x13^2 * (1 + x21^2/y21^2) =
multiply both sides by y21^2
x13^2 * (y21^2 + x21^2) = |1->3|^2 * y21^2
plug in Pythagorean theorem of 2->1
x13^2 * |2->1|^2 = |1->3|^2 * y21^2
take square root of both sides
x13 * |2->1| = |1->3| * y21
divide both sides by the length of 2->1
x13 = (|1->3|/|2->1|) *y21
lets call the ratio of |1->3| to |2->1| psi
x13 = psi * y21
check the signs
when y21 is negative, x13 will be negative
when y21 is positive, x13 will be negative
x13 = psi * y21
压缩
x21 = x1 - x2
y21 = y1 - y2
|2->1| = sqrt( x21^2 + y^21^2 )
|1->3| = N/2
psi = |1->3|/|2->1|
y13 = -psi * x21
x13 = psi * y21
我通常不会这样做,但我在工作中解决了这个问题,并且认为彻底讲解它将有助于巩固我的知识。