Δ The angles at the lateral side of the trapezoid add up to 180∘ (as interior alternate angles). Therefore, there are also angles 180∘−60∘=120∘ and 180∘−130∘=50∘ in the trapezoid. Thus, all four angles have been found. ◃
Source: NuminaMath-1.5,
licensed Apache-2.0.
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