tan θ = cosx ∈[-1 ,1]
θ ∈ [0 ,π/4] ∪ [3π/4 ,π]已知直线L；4X+3Y=c被两坐标轴截得线段长为1则c得值为？这题会做么？ 还有曲线3x^2-5x+1。在点1处的切线方程？x = 0 , y = c/3y = 0 , x = c/4√[(c/3)² + (c/4)²] = 1c = ±12/5f(x) = 3x² - 5x + 1f(1) = -1f'(x) = 6x - 5k = f'(1) = 1y - f(1) = k(x - 1)y + 1 = x - 1x - y - 2 = 0圆x^2+y^2-4x+6y-3=0上到x轴距离等于1的点有几个？y = 1x² + 1 - 4x + 6 - 3 = 0x² - 4x + 4 = 0x = 2y = -1x² + 1 - 4x - 6 - 3 = 0x² - 4x + -8 = 0x = 2 ± 2√3共3个点 (1 , 2) , (-1 , 2+2√3) , (-1 , 2-2√3)距离x为什么y等于1呢？距离x轴等于1的点的纵坐标为1或-1均在y = 1 或 y = -1 上。