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प्रश्न
Without using trigonometric tables, prove that:
cos275° + cos215° = 1
उत्तर
LHS = cos275° + cos215°
= cos2(`90^circ - 15^circ) + cos^2 15^circ`
= `sin^2 15^circ + cos^2 15^circ`
= 1
= RHS
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