Answer: 100 i think, but am not sure.
Step-by-step explanation:
The formula for area of a rectangle is A=l*w. Since the area is 84, then you can use the A=l*w formula. 84 = x(x+8) would be the equation to solve for x.
Now, you need to put the equation in standard form. So, x2 + 8x - 84 = 0.
Since you can't solve this quadratic using factoring, you need to complete the square.
To complete the square you need to add 84 to both sides. Now you have x2 + 8x = 84. Take the coefficient for the x term (8) and divide by 2. Now square it. That would be 42, so 16. Now you have x2 +8x +16 = 100.
Factor x2 +8x +16, so (x+4)2 = 100
If you use the square root property, you have x+4 = 10. Therefore, x = 6 (the short side) and 14 is the long side.
