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Question
Without using trigonometric identity , show that :
`cos^2 25^circ + cos^2 65^circ = 1`
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Solution
Consider `cos^2 25^circ + cos^2 65^circ`
⇒ `cos^2(90^circ - 65^circ) + cos^2 65^circ`
⇒ `sin^2 65^circ + cos^2 65^circ = 1`
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