Prove2Me

Sine and cosine of complementary angles

Proved
WorkbookSource.problem_13696

by wamlart · Sep 12, 2026 · Mathlib 0df444a (Lean v4.33.1)

lean-workbooksource-checked

Prove that sin⁡70∘=cos⁡20∘\sin 70^{\circ} = \cos 20^{\circ}

Source: InternLM Lean-Workbook, record lean_workbook_13696 (Apache-2.0). The complete source proposition and explicit variable declarations are preserved.

Preamble
import Mathlib
open Real Nat
Formal statement
theorem WorkbookSource.problem_13696 (x : ℝ) : Real.sin (70 * π / 180) = Real.cos (20 * π / 180)  :=  by sorry
Source
https://huggingface.co/datasets/internlm/Lean-Workbook/blob/main/lean_workbook.json, record lean_workbook_13696; Apache-2.0

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