Question 903826
16:9 means

width = 16x
height = 9x

for some number x


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a^2 + b^2 = c^2


(16x)^2 + (9x)^2 = 42^2


256x^2 + 81x^2 = 1764


337x^2 = 1764


x^2 = 1764/337


x^2 = 5.23442136498517 (this is approximate)


x = sqrt(5.23442136498517) (this is approximate)


x = 2.28788578495194 (this is approximate)


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Width: 16x = 16*2.28788578495194 = 36.606172559231


Height: 9x = 9*2.28788578495194 = 20.5909720645674


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Summary:



Width: 36.606 inches


Height: 20.591 inches


Answers are approximate. I rounded the final values to 3 decimal places