圖片:
已知
小三角形 A^2+B^2=X^2
COSα=A/X => A=X*COSα
大三角形 (A+D)^2+B^2=R^2
解步驟
大三角直角關(guān)系解出:
A^2+2*A*D+D^2+B^2=R^2
由A=X*COSα代入變?yōu)椋?br />A^2+2*X*C0Sα*D+D^2+B^2=R^2
由 A^2+B^2=X^2,消去 A^2+B^2:
X^2+2*X*D*C0Sα+D^2=R^2
湊多項(xiàng)式的平方式,等式兩邊同時(shí)減去D^2,加(D*C0Sα)^2 變?yōu)椋?br />X^2+2*X*(D*C0Sα)+(D*C0Sα)^2=R^2-D^2+(D*C0Sα)^2
等式左邊合成多項(xiàng)式的平方,變?yōu)椋?br />(X+D*C0Sα)^2=R^2-D^2+(D*C0Sα)^2
等式兩邊開(kāi)平方跟,變?yōu)椋?br />X+D*C0Sα=√(R^2-D^2+(D*C0Sα)^2)
等式兩邊同時(shí)減去D*C0Sα,變?yōu)椋?br />X=√(R^2-D^2+(D*C0Sα)^2)-D*C0Sα