2) What is the five-digit number, no zeroes, in which the second digit is three times the first, the third is one more than the
1 answer:
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A
using the Cosine rule in ΔSTU
let t = SU, s = TU and u = ST, then
t² = u² + s² - (2us cos T )
substitute the appropriate values into the formula
t² = 5² + 9² - (2 × 5 × 9 × cos68° )
= 25 + 81 - 90cos68°
= 106 - 33.71 = 72.29
⇒ t = ≈ 8.5 in → A