Answer:
a. 7 by 21
b. a(-12, 2), b(-12, -5), c(9, -5)
Step-by-step explanation:
AD is 3 times the length of AB. X can be the length of AB. Then 3x would be the length of AD. The perimeter is 56, which would also be 3x + x + 3x + x which is 8x. This gives us 8x = 56, meaning that x is 7, or the length of AB is 7. Because AD is 3 times the length of AB (which is 7), AD = 21. Therefore, the dimensions of the rectangle ABCD is 7 by 21.
Coordinates of A have to be 21 units away from D since AD = 21. It goes in the left direction, meaning that 21 is subtracted from 9 (since this is a horizontal edge involving x coordinates) while the y value remains the same. The result is (-12, 2). For coordinate B, it has to be 7 units away from A downwards since AB = 7. This means that you subtract 7 from 2 (involving only the y coordinates), resulting in (-12, -5). For coordinate C, it has to be 21 units from B since BC = AD = 21. Because C is right compared to B, you have to add 21 to -12 (involving only the x coordinate) resulting in (9, -5).