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Diagonal divide the rectangle in two triangles, each of which is (3-4-5) right angled triangle.
Therefore, the dimensions of each triangle are 3x, 4x and 5x inches, where x is their common measure, now unknown.
We will find x very easy by noticing that 5x = 55 inches; hence x = 11 inches.
Therefore, the dimensions of the TV are 3*11 = 33 inches and 4*11 = 44 inches. ANSWER
Solved (mentally).