Answer:
length = 32.8 ft
height = 13.8 ft
Step-by-step explanation:
35 ft is a measurement of the diagonal of the screen
21:9 is the ratio of the length:height (L:H)
Use pythagorean theorem:
35² = L² + H²
21/9 = L/H
L = H(21/9) substitute into 1st equation
35² = (H(21/9))² + H²
35² = H²(21/9)² + H² rearrange and solve for H
H²(1 + (21/9)²) = 35²
H² = (35²) / (1 + (21/9)²) = 190.0862
H = √190.0862 = 13.787 ≈ 13.8 ft
L = (13.787)(21/9) = 32.77 ≈ 32.8 ft