cho tam giác ABC cân tại A,đường cao AD. O là trung điểm AC. D đối xứng với E qua O. Chứng minh AECD là hình chữ nhật

What is the missing value in the proportion 4/5 = x/30

What is the equation of the line that passes through (-3, -1) and has a slope of 2/5 ? put your answer in slope-intercept form. a y= 2/5x+1/5 b y=2/5x-1/5 c y=-2/5x-1/5

The length of a rectangular board is 3 feet less than twice its width. a second rectangular board is such that each of its dimensions is the reciprocal of the corresponding dimensions of the first rectangular board. if the perimeter of the second board is one-fifth the perimeter of the first, what is the perimeter of the first rectangular board?