Math, asked by ranjithkrish447, 1 month ago

prove that cos20° cos70°=√2 cos 25°

Answers

Answered by RvP10

2

Answer:

cos20 = cos(45-25)

= cos45cos25+sin45sin25

cos70 = cos(45+25)

= cos45cos25-sin45sin25

cos20 + cos70

= cos45cos25+sin45sin25 +cos45cos25-sin45sin25

=2cos45cos25

=2 x1/√2xcos25

=√2cos25

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