If the area of the region \(x, y) : |x - 5| y 4 x\ is A, then 3A is equal to .
Answer
368
Solution
Intersections of y = 4 x with y = |x - 5| (put x = t):
x 5: t2 - 5 = 4t t2 - 4t - 5 = 0 t = 5 x = 25
x < 5: 5 - t2 = 4t t2 + 4t - 5 = 0 t = 1 x = 1
Between x = 1 and x = 25, 4 x |x - 5|.
A = 125 4 x dx - 125 |x - 5| dx
125 4 x dx = 83 [x3/2 ]125 = 83(125 - 1) = 9923
125 |x - 5| dx = 15 (5 - x) dx + 525 (x - 5) dx = 8 + 200 = 208
A = 9923 - 208 = 3683
3A = 368
Answer: 368