Answer:
a = 9 , b = 5 , c = 25
Explanation:
using the Cosine rule in the triangle
a² = b² + c² - 2bc cosA
where a is the side opposite ∠ A and b, c the sides adjacent to ∠ A
here
a = y , b = x + 5 , c = 3x and A = Θ , then
y² = (x + 5)² + (3x)² - [ 2(x + 5) × 3x × cosΘ ]
y² = x² + 10x + 25 + 9x² - [ 6x(x + 5) ×
]
y² = 10x² + 10x + 25 - x(x + 5)
y² = 10x² + 10x + 25 - x² - 5x
y² = 9x² + 5x + 25 ← in the form y² = ax² + bx + c
with a = 9 , b = 5 , c = 25