a=5
b = ?
[(5*b - b^2/2)] / [2*(sqrt(25 - (b^2/4)))] =4/3, solve for b
Solve for b:
(5 b - b^2/2)/(2 sqrt(25 - b^2/4)) = 4/3
Cross multiply:
3 (5 b - b^2/2) = 8 sqrt(25 - b^2/4)
3 (5 b - b^2/2) = 8 sqrt(25 - b^2/4) is equivalent to 8 sqrt(25 - b^2/4) = 3 (5 b - b^2/2):
8 sqrt(25 - b^2/4) = 3 (5 b - b^2/2)
Raise both sides to the power of two:
64 (25 - b^2/4) = 9 (5 b - b^2/2)^2
Expand out terms of the left hand side:
1600 - 16 b^2 = 9 (5 b - b^2/2)^2
Expand out terms of the right hand side:
1600 - 16 b^2 = (9 b^4)/4 - 45 b^3 + 225 b^2
Subtract (9 b^4)/4 - 45 b^3 + 225 b^2 from both sides:
-(9 b^4)/4 + 45 b^3 - 241 b^2 + 1600 = 0
The left hand side factors into a product with five terms:
-1/4 (b - 10) (b - 8) (9 b^2 - 18 b - 80) = 0
Multiply both sides by -4:
(b - 10) (b - 8) (9 b^2 - 18 b - 80) = 0
Split into three equations:
b - 10 = 0 or b - 8 = 0 or 9 b^2 - 18 b - 80 = 0
Add 10 to both sides:
b = 10 or b - 8 = 0 or 9 b^2 - 18 b - 80 = 0
Add 8 to both sides:
b = 10 or b = 8 or 9 b^2 - 18 b - 80 = 0
Divide both sides by 9:
b = 10 or b = 8 or b^2 - 2 b - 80/9 = 0
Add 80/9 to both sides:
b = 10 or b = 8 or b^2 - 2 b = 80/9
Add 1 to both sides:
b = 10 or b = 8 or b^2 - 2 b + 1 = 89/9
Write the left hand side as a square:
b = 10 or b = 8 or (b - 1)^2 = 89/9
Take the square root of both sides:
b = 10 or b = 8 or b - 1 = sqrt(89)/3 or b - 1 = -sqrt(89)/3
Add 1 to both sides:
b = 10 or b = 8 or b = 1 + sqrt(89)/3 or b - 1 = -sqrt(89)/3
Add 1 to both sides:
b = 10 or b = 8 or b = 1 + sqrt(89)/3 or b = 1 - sqrt(89)/3
(5 b - b^2/2)/(2 sqrt(25 - b^2/4)) ⇒ (5 8 - 8^2/2)/(2 sqrt(25 - 8^2/4)) = 4/3
4/3 ⇒ 4/3 ≈ 1.33333:
So this solution is correct
(5 b - b^2/2)/(2 sqrt(25 - b^2/4)) ⇒ (5 10 - 10^2/2)/(2 sqrt(25 - 10^2/4)) = (undefined)
4/3 ⇒ 4/3 ≈ 1.33333:
So this solution is incorrect
(5 b - b^2/2)/(2 sqrt(25 - b^2/4)) ≈ -1.33333
4/3 ⇒ 4/3 ≈ 1.33333:
So this solution is incorrect
(5 b - b^2/2)/(2 sqrt(25 - b^2/4)) ≈ 1.33333
4/3 ⇒ 4/3 ≈ 1.33333:
So this solution is correct
The solution is:
b = 8 - The 3rd side of isosceles triangle.