Algebra, grade 9, quarter IV, BZH 1
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00:00 Write the sum as: cos(x +1) cos(x -1) ...
02:41 Show that the equation is true: cos84°+cos 36°−cos24°=0 ...
04:34 Prove the equality: (sin2α+sin2β)² + (cos2α−cos2β)² = 4cos²(α−β) ...
09:12 Find the value of the expression sin75°sin15°. ...
10:36 Simplify the expression: ...